Development reference: Difference between revisions

Latest revision as of 23:15, 25 November 2023

Design, programming and version control.

Patterns

Major Objects

Quick-http

Continuous Integration

Architecture of major open source apps

Security

Model View Controller

nosql enhances, not replaces, SQL
Not all data should be denormalized, and not all data should be normalized. The optimal mix considers the extent of the data. Precise schemas are good when not overdone When a container has an array with a large number of elements, it should be normalized Sparse data and heterogeneous data are the best candidates for denormalization Postgres with JSON allows an elegant combination of nosql and SQL.

Web design mantra
DESIGN INPUT TO THE INPUT DEVICE respect the input device detect it and use a reasonable default guess allow manual override [mouse/pen]...[finger] sm-md-lg ... sm-md-lg DESIGN VISUALS TO THE SCREEN high-res = SHOW LOTS OF DETAIL responsive, zoomable

git central shared repository
Use bare repos for any central shared repositories. Use the [####.git] suffix on bare repo names. Bare repositories are designed to be shared. Maintenance on the central server is easier because you don't have local files to manage permissions or constant flux. Plus, you can always have a second repo on the central server where you check out a specific branch (e.g. to serve up with apache). If you want a dynamically updated central repo, clone the ###.git repo to ###, and add a post-receive hook (see bitpost quick-http.git for a good example). To configure the repo as shared: git config core.sharedRepository true To set it on a new git repo during initial setup, make sure devs are in the same group, and use: git init --shared=group

Occam's razor
Among competing hypotheses, the one with the fewest assumptions should be selected.

C++

Deleting multiple elements in a collection
For sequences (vector, list...), best practice is to use the erase-remove STL pattern For associative containers (set, map...): just recurse and remove iterators, they won't muck up the sequence. example See MemoryModel::saveDirtyObjectsAsNeeded() for example code.

c++ Create a portable C/C++ project

Use QtCreator + CMake, both available everywhere!

   set up:
       create a Qt project as: New Project-> Non-Qt/Plain C Project (CMake Build)
           pick the PARENT and use the name of the existing folder
           set up a build folder in the existing folder, called (base)/qtcreator-release-build
           it creates CMakeLists.txt (THIS IS BASICALLY THE PROJECT FILE!)
           also creates main.c or something
           build it!  make sure it works
           NOW we can edit CMakeLists.txt - change . to ./src to get it to scan the src folder for code!
           and easily add "known" libs!  this was all i needed:
               TARGET_LINK_LIBRARIES(${PROJECT_NAME} pthread websockets)
           make sure it builds
           now we want a DEBUG build as well!
           Projects->Build&Run->pick Build in weird Build/Run pillbox->Edit build configs:
               Rename: release
               CMake build dir: Make sure build dir is set to release ie qtcreator-debug-build
               Add: Clone: release, name: debug
                   for debug, add a custom build step BEFORE make step:
                       command: /usr/bin/cmake
                       args: -DCMAKE_BUILD_TYPE=Debug .
                       working dir: %{buildDir}
                       (add it, and move it up above make)
                       (build em both)
           Projects->Build&Run->pick Run in weird Build/Run pillbox
               Run Configuration: rename to "{...} release"
               clone it into "{...} debug"
               change working dir to match Build path
               change any needed params
   Now you should have build+run debug+release configurations, selectable in the weird project icon in bottom of left-side toolbar ("mode selector")

c++ in-memory storage of "major" objects

   OBSERVATION ONE

   Consider An Important Qt Design: QObjects cannot normally be copied
       their copy constructors and assignment operators are private
       why?  A Qt Object...
           might have a unique QObject::objectName(). If we copy a Qt Object, what name should we give the copy?
           has a location in an object hierarchy. If we copy a Qt Object, where should the copy be located?
           can be connected to other Qt Objects to emit signals to them or to receive signals emitted by them. If we copy a Qt Object, how should we transfer these connections to the copy?
           can have new properties added to it at runtime that are not declared in the C++ class. If we copy a Qt Object, should the copy include the properties that were added to the original?
   in other words, a QObject is a pretty serious object that has the ability to be tied to other objects and resources in ways that make copying dangerous
   isn't this true of all serious objects?  pretty much

   OBSERVATION TWO

   if you have a vector of objects, you often want to track them individually outside the vector
   if you use a vector of pointers, you can move the object around much more cheaply, and not worry about costly large vector reallocations
   a vector of objects (not pointers) only makes sense if the number of objects is initially known and does not change over time

   OBSERVATION THREE

   STL vectors can store your pointers, iterate thru them, etc.
   for a vector of any substantial size, you want to keep objects sorted so you can find them quickly
   that's what my sorted_vector class is for; it simply bolts vector together with sort calls and a b_sorted status
   following STL practices, to get sorting, you have to provide operator< for whatever is in your vector
   BUT... you are not allowed to do operator<(const MyObjectPtr* right) because it would require a reference to a pointer which is not allowed
   BUT... you can provide a FUNCTOR to do the job, then provide it when sorting/searching
   a functor is basically a structure with a bool operator()(const MyObjectPtr* left, const MyObjectPtr* right)

   OBSERVATION FOUR

   unordered_set works even better when combining frequent CRUD with frequent lookups

   SUMMARY
   Dealing with tons of objects is par for the course in any significant app.
   Finding a needle in the haystack of those objects is also standard fare.
   Having multiple indices into those objects is also essential.
   Using unordered_set with object pointers and is very powerful.

c++ stl reverse iterator skeleton
From SGI... reverse_iterator rfirst(V.end()); reverse_iterator rlast(V.begin()); while (rfirst != rlast) { cout << *rfirst << endl; ... rfirst++; }

c++ stl reading a binary file into a string

   std::ifstream in("my.zip",std::ios::binary);
   if (!in)
   {
      std::cout << "problem with file open" << std::endl;
      return 0;
   }
   in.seekg(0,std::ios::end);
   unsigned long length = in.tellg();
   in.seekg(0,std::ios::beg);
 
   string str(length,0);
   std::copy( 
       std::istreambuf_iterator< char >(in) ,
       std::istreambuf_iterator< char >() ,
       str.begin() 
   );

For more, see c++ stl reading a binary file

C/C++ best-in-class tool selection
I need to have easy setup of debug-level tool support for portable C++11 code. And I need to decide and stick to it to be efficient. Compiler selection linux and mac: gcc windows: Visual Studio IDE selection linux and mac: Qt Creator windows: Qt Creator (OR Visual Studio OR eclipse?) Debugger selection linux and mac: Qt Creator windows: Qt Creator (OR Visual Studio OR eclipse?)

c++11

c++11 include base constructor (etc) in derived class

The awesome C++11 way to steal the constructor from the base class, oh man I've been waiting for this one...

 class HttpsServer : public Server<HTTPS>
 {
   // DOES THIS FOR YOU!
   /*
   HttpsServer(unsigned short port, size_t num_threads, const std::string& cert_file, const std::string& private_key_file)
   :
       // Call base class
       Server<HTTPS>::Server(port, num_threads, cert_file, private_key_file)
   {}
   */
   using Server<HTTPS>::Server;
   ....

c++11 containers
sorted_vector	use when doing lots of unsorted insertions and maintaining constant sort would be expensive; vector is good for a big pile of things that only occasionally needs a sorted lookup
map	sorted binary search tree; always sorted by key; you can walk through in sorted order (choose unordered if not needed!)
multimap	same as map but allows dupe keys (not as common)
unordered_map	hashmap; always sorted by key; additional bucket required for hash collisions; no defined order when walking through
unordered_multimap	same as map but allows dupe keys; dupes are obviously in the same bucket, and you can walk just the dupes if needed
set multiset unordered_set unordered_multiset	sets are just like maps, except the key is embedded in the object, nice for encapsulation. Items must be const (!) since they are the key - sounds bad, but this is mitigated by the mutable keyword. You can use mutable on the variables that are not part of the key to remove the const. This changes the constness of the object from binary (completely const) to logical (constness is defined by the developer). So... set is a good way to achieve both encapsulation and logical const - make const work for you, not against! :-)
set (etc.) of pointers	sets of pointers are the pinnacle of object stores The entire object can be dereferenced and accessed then without const issues. A pointer functor can be provided that does a sort by dereferencing the pointer to the object. Two requirements: you must make sure yourself that you do not change the key values - you can mark them const, provided in constructor; you must create sort/equal/hash functors that dereference the pointers to use object contents (the default will be by pointer address). The arguably biggest advantage, as a result, is that you can create multiple sets to reference the same group of objects with different sort funtors to create multiple indices. You just have to manage the keys carefully, so that they don't change (which would invalidate the sorting). The primary container can manage object allocation; using a heap-based unique_ptr allocation map vs key redux use a key in the set, derive a class from it with the contents + small key + encapsulation - requires mutable to solve the const problem use a key in the set, key includes a mutable object + encapsulation - weird bc everything uses a const object but we have const functions like save() that change the mutable subobject use a map + small key - no encapsulation, have to deal with a pair instead of an object can we just put a ref to key in the value? sure why not - err, bc we don't have access to it + solves const problem bc value is totally mutable by design + we can have multiple keys - and the value can have multiple refs to them + simpler equal and hash functions map: create an object with internal key(s) create map index(es) with duplicate key values outside the object - dupe data is the downside use set(s) with one static key for find(): create an object with internal key(s) create set index(es) with specific hash/equals functor(s) when finding, use one static key object (even across indexes!) so there isn't a big construction each time; just set the necessary key values that proves difficult when dealing with member vars that are references but to solve it, just set up a structure of dummy static key objects that use each other; then provide a function to setKey(Object& keyref) { keyref_ = keyref; } nope, can't reassign refs the solution: use pointers not references yes that's right just do it apparently there was a reason i was anti-reference for all those years two reasons to use pointers: dynamically allocated reassignment required there ya go. simple. get it done. when accessing find results from the set, use a const_cast on the object! WARNING: a separate base class with the key sounds good... but fails when you have more than one index on the object. just use a static key object for them all!

c++11 example for large groups of objects with frequent crud AND search
Best solution is an unordered set of pointers: typedef boost::unordered_set<MajorObject*> MajorObjects;

c++11 example for large groups of objects with infrequent crud and frequent search
Best solution is a vector of pointers sorted on demand (sorted_vector): TODO

c++11 example to associate two complex objects (one the map key, one the map value)

Use unordered_map with a custom object as key. You must add hash and equals functions. Boost makes it easy:

static bool operator==(MyKeyObject const& m1, MyKeyObject const& m2)
{
    return 
            m1.id_0 == m2.id_0
        &&  m1.id_1 == m2.id_1;
}
static std::size_t hash_value(MyKeyObject const& mko)
{
    std::size_t seed = 0;
    boost::hash_combine(seed, mko.id_0);
    boost::hash_combine(seed, mko.id_1);
    return seed;
}
typedef boost::unordered_map<MyKeyObject, MyValueObject*> MyMap;

Note that you can extend this to use a pointer to a key object, whoop.

c++11 example for multiple unordered_set indexes into one group of objects
Objects will be dynamically created. One set should include them all and be responsible for memory allocation cleanup: TODO

c++11 example for set with specific sorting

Use set with a specific sort functor. You can create as many of these indexes as you want!

struct customers_set_sort_functor
{
    bool operator()(const MyObject* l, const MyObject* r) const
    {
        // the id is the key
        return l->id_ < r->id_;
    }
};
typedef set<MyObject*,myobject_sort_by_id_functor> MyObjectsById;

c++11 loop through vector to erase some items
Note that other containers' iterators may not be invalidated so you can just erase() as needed... For vectors, you have to play with iterators to get it right - watch for proper ++ pre/postfix! for (it = numbers.begin(); it != numbers.end(); ) // NOTE we increment below, only if we don't erase { if (it.no_good()) { numbers.erase(it++); // NOTE that we ERASE THEN INCREMENT here. } else { ++it; } } I thought I had always looped backwards to do this, I think* that's ok too, but I don't see it used in my code, I think I'll avoid. :-)

c++11 range based for loop, jacked with boost index if needed
No iterator usage at all. Nice at times, not enough at others. Make SURE to always use a reference or you will be working on a COPY. Make it const if you aren't changing the object. for (auto& mc : my_container) mc.setString("default"); for (const auto& cmc : my_container) cout << cmc.asString(); boost index can give you the index if you need it, sweet: #include <boost/range/adaptor/indexed.hpp> ... for (const auto &element: boost::adaptors::index(mah_container)) cout << element.value() << element.index();

c++11 for loop using lambda
This C++11 for loop is clean and elegant and a perfect way to check if your compiler is ready for c++11: vector<int> v; for_each( v.begin(), v.end(), [] (int val) { cout << val; } ); This is using a lambda function, we should switch from iterators and functors to those - but not quite yet, since we're writing cross-platform code. Do not touch this until we can be sure that all platforms provide compatible C++11 handling.

c++11 integer types

I really like the "fast" C++11 types, that give best performance for a guaranteed minimum bit width.

Use them when you know a variable will not exceed the maximum value of that bit width, but does not have to be a precise bit width in memory or elsewhere.

Pick specific-width fields whenever data is shared with other processes and components and you want a guarantee of its bit width.

And when using pointer size and array indices you should use types defined for those specific situations.

FAST types:

   int_fast8_t
   int_fast16_t                fastest signed integer type with width of
   int_fast32_t                at least 8, 16, 32 and 64 bits respectively
   int_fast64_t

   uint_fast8_t
   uint_fast16_t               fastest unsigned integer type with width of
   uint_fast32_t               at least 8, 16, 32 and 64 bits respectively
   uint_fast64_t

SMALL types:

   int_least8_t
   int_least16_t               smallest signed integer type with width of
   int_least32_t               at least 8, 16, 32 and 64 bits respectively
   int_least64_t

   uint_least8_t
   uint_least16_t		smallest unsigned integer type with width of
   uint_least32_t		at least 8, 16, 32 and 64 bits respectively
   uint_least64_t

EXACT types:

   int8_t                      signed integer type with width of
   int16_t                     exactly 8, 16, 32 and 64 bits respectively
   int32_t                     with no padding bits and using 2's complement for negative values
   int64_t                     (provided only if the implementation directly supports the type)

   uint8_t                     unsigned integer type with width of
   uint16_t                    exactly 8, 16, 32 and 64 bits respectively
   uint32_t                    (provided only if the implementation directly supports the type)
   uint64_t

SPECIFIC-USE types:

   intptr_t                    integer type capable of holding a pointer
   uintptr_t                   unsigned integer type capable of holding a pointer 
   size_t                      unsigned integer type capable of holding an array index (same size as uintptr_t)

C++11 scoped enumeration
C++11 has scoped enumeration, which lets you specify the SPECIFIC VARIABLE TYPE for the enum. Perfect, let's use uint_fast32_t. enum class STRING_PREF_INDEX int_fast32_t: { ... }; Unfortunately, gcc gives me a scary warning, and stuff fails. For some reason, it does not know about the provided type, although it is definitely defined. Revisit this later if you have time. warning: elaborated-type-specifier for a scoped enum must not use the ‘class’ keyword Old skool is still cool: typedef enum { // assert( SP_COUNT == 2 ); SP_FIRST = 0 , SP_SOME_PREF = SP_FIRST , SP_ANOTHA , SP_COUNT } STRING_PREF_INDEX;

boost

boost release and debug build for linux

   # download latest boost, eg: boost_1_59_0 
   m@wallee:~/development$ 7z x boost_1_59_0.7z
   rm boost && ln -s boost_1_59 boost
   cd boost
   build_boost_release_and_debug.sh
   # IMPORTANT: then patch .bashrc as instructed
   #     cmake-###/clean.sh and cmake-###/build.sh are customized to match
   #     (and older eclipse and server/nix/bootstrap.sh)

To upgrade a CMake project:

   cd cmake-###/
   ./clean.sh
   ./build.sh

To upgrade an older autotools project:

   cd nix
   make distclean  # removes nasty .deps folders that link to old boost if you let them
   make clean      # removes .o files etc
   cd ../build-Release && make distclean && make clean
   cd ../build-Debug && make distclean && make clean
   cd ..
   ./bootstrap force release
   ./bootstrap force debug

boost release and debug build for Windows

Open a VS2015 x64 Native Tools Command Prompt.

EITHER: for new installs, you have to run bootstrap.bat first, it will build b2; OR: for reruns, remove boost dirs: [bin.v2, stage]. Then build 64-bit:

cd "....\boost_1_59_0"
b2 toolset=msvc variant=release,debug link=static address-model=64
rem trying to avoid excessive options, assuming I don't need these: threading=multi
(old stuff)
      --toolset=msvc-14.0 address-model=64 --build-type=complete --stagedir=windows_lib\x64 stage
      Now open VS2013 x86 Native Tools Command Prompt and build 32-bit:
      cd "C:\Michael's Data\development\sixth_column\boost_1_55_0"
      bjam --toolset=msvc-12.0 address-model=32 --build-type=complete --stagedir=windows_lib\x86 stage

boost regex (very similar to c++11, with LESS BUGS and MORE POWER)

boost regex does everything you could need, take your time to get it right

regex_search will work hard to find substrings, while regex_match requires your regex to match entire input
smatch is a great way to get back a bunch of iterators to the results

example:

   virtual bool url_upgrade_any_old_semver(string& url)
   {
     // Perform a regex to update the embedded version if needed.
     // We have to see if (1) we have a semver and (2) it is not the current semver.
     // Only then do we take action.
     boost::regex regex("/([v0-9.]+?)/(.*)");
     boost::smatch sm_res;
     if (boost::regex_match(url,sm_res,regex,boost::match_default))
     {
       string incoming_semver(sm_res[1].first,sm_res[1].second);
       if (incoming_semver != semanticVersion())
       {
         url = string("/")+semanticVersion()+"/"+string(sm_res[2].first,sm_res[2].second);
         return true;
       }      
     }
     return false;
   }

results:

     original string:    string(sm_res[0].first,sm_res[0].second);
     first group:        string(sm_res[1].first,sm_res[1].second);
     second group:       string(sm_res[2].first,sm_res[2].second);
     etc.

C++ libraries

String escape formatting across different languages and systems
c++ to JSON: always use nlohmann::json j.dump() to encode, to ensure strings are properly escaped JSON to c++: always use nlohmann::json j.parse() " c++ to Javascript: use raw_to_Javascript() to properly escape c++ to sqlite: use SqliteLocalModel::safestr(), which uses double_doublequotes(str)

Postgres

Simple-Web-Server

Robot Operating System

C++ https libraries

Configure Qt development on Windows + Mac + linux

Build the TagLib library with Visual Studio 2013

C/C++ building/linking

gcc makefile pain
I went through a LOT of pain to determine that gcc requires libraries to be listed AFTER the source and output parameters set LD_LIBRARY_PATH to point to your libs if they are not in system location Make sure Makefile uses TABS NOT SPACES. it's a FACT OF LIFE. hate it if you want. plenty more things to hate about linux/C as well.

gcc install multiple versions in ubuntu (4 and 5 in wily, eg)

My code will not compile with gcc 5, the version provided with Ubuntu wily.

It gives warnings like this:

/home/m/development/boost_1_59_0/boost/smart_ptr/shared_ptr.hpp:547:34: warning: ‘template<class> class std::auto_ptr’ is deprecated [-Wdeprecated-declarations]

and outright errors like this:

depbase=`echo AtServer.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`;\
g++ -DPACKAGE_NAME=\"at_server\" -DPACKAGE_TARNAME=\"at_server\" -DPACKAGE_VERSION=\"1.0\" -DPACKAGE_STRING=\"at_server\ 1.0\" -DPACKAGE_BUGREPORT=\"[email protected]\" -DPACKAGE_URL=\"\" -DPACKAGE=\"at_server\" -DVERSION=\"1.0\" -I. -I../../src  -I/home/m/development/Reusable/c++ -I/home/m/development/Reusable/c++/sqlite -std=c++11 -I/home/m/development/boost_1_59_0  -ggdb3 -O0 -std=c++11 -MT AtServer.o -MD -MP -MF $depbase.Tpo -c -o AtServer.o ../../src/AtServer.cpp &&\
mv -f $depbase.Tpo $depbase.Po
In file included from /usr/include/c++/5/bits/stl_algo.h:60:0,
                from /usr/include/c++/5/algorithm:62,
                from /usr/include/c++/5/ext/slist:47,
                from /home/m/development/boost_1_59_0/boost/algorithm/string/std/slist_traits.hpp:16,
                from /home/m/development/boost_1_59_0/boost/algorithm/string/std_containers_traits.hpp:23,
                from /home/m/development/boost_1_59_0/boost/algorithm/string.hpp:18,
                from /home/m/development/Reusable/c++/utilities.hpp:4,
                from ../../src/MemoryModel.hpp:11,
                from ../../src/SqliteLocalModel.hpp:13,
                from ../../src/AtServer.cpp:70:
/usr/include/c++/5/bits/algorithmfwd.h:573:13: error: initializer provided for function
    noexcept(__and_<is_nothrow_move_constructible<_Tp>,
            ^
/usr/include/c++/5/bits/algorithmfwd.h:582:13: error: initializer provided for function
    noexcept(noexcept(swap(*__a, *__b)))

You can set up the update-alternatives tool to switch out the symlinks:

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.9 60 --slave /usr/bin/g++ g++ /usr/bin/g++-4.9
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-5 20 --slave /usr/bin/g++ g++ /usr/bin/g++-5

BUT that seems BAD to me to switch out the compiler used by the SYSTEM. Instead, we should specify the compiler required by the PROJECT. This is supposed to do it, but it still uses /usr/include/c++/5, which seems wrong, and gives me errors:

CC=gcc-4.9

git

Debugging

Chrome capture large JSON variable
This is just pointlessly bizarre: hit a breakpoint in the chrome debugger right-click a variable and say "copy to global variable" (console will show name, typically "temp1") push the variable to the clipboard by typing this in the console: copy(temp1)

Visual Studio Code capture large string variable
While debugging, you can use the Debug Console to print memory, including the content of strings that are clipped by default in the variables and watch windows. View > Open View > Debug Console From there, send gdb a command to print memory – 300 characters of a string in this example: -exec x/300sb Query.c_str()

Qt Creator conditional breakpoint
To break on line number with string condition: Set the breakpoint on the line as usual: F9 or click in left border In the breakpoints list, rclick Edit Add a condition; to break on a string value, THIS WORKS: ((int)strcmp(strSymbol.c_str(), "GMO")) == 0 BUT THERE IS A PRICE TO PAY. qt/gcc won't continue properly, unless you sset ANOTHER common breakpoint, hit it, and resume from that. It appears gcc continues (we hit the breakpoint after all), but qt does no logging or debugging, bah

Qt Creator and linux debug libraries

I was able to build lws in debug, install in /usr/local, then I could step right into its code

m@case:~/development/causam/git/np/nop-bigress-client-c$ ./build_lws_debug
 Install the project...
 -- Install configuration: "DEBUG"
 -- Installing: /usr/local/lib/pkgconfig/libwebsockets.pc
 -- Installing: /usr/local/lib/libwebsockets.a
 -- Up-to-date: /usr/local/include/libwebsockets.h
 (etc)

Signals: At some point I needed to force gdb to pass SIGINT, SIGPIPE... signals to the app instead of gdb, after ssl kept causing Qt to pop a message and break in the debugger. To do so:

       Qt Creator->Options->Debugger->
           [ ] Show a message box when receiving a signal
           Debugger Helper Customization: handle SIGPIPE pass nostop noprint

You should be able to install debug builds of libraries into /usr/local (as mentioned above). Older notes if you can't get that going: To debug into an included library that is not installed system-wide:

use Tools->Options->General->Source Paths Map
 source: /home/m/development/causam/git/nop-bigress-client-c/cmake-debug
   that's the COMPLETE PATH TO DEBUG EXE
 target: /home/m/development/causam/git/libwebsockets-master/lib
   at first i thought this would work: /usr/local/lib
   but i did a static build so i needed teh actual exe!  COOL

QT Creator valgrind EASY
Valgrind is easy to use. Just find debugger pane top-left dropdown, switch mode from Debugger to Memcheck, and restart debugger.

c/c++ gdb debugging

(gdb) help break
Set breakpoint at specified line or function.
Argument may be line number, function name, or "*" and an address.
If line number is specified, break at start of code for that line.
If function is specified, break at start of code for that function.
If an address is specified, break at that exact address.
With no arg, uses current execution address of selected stack frame.
This is useful for breaking on return to a stack frame.

Multiple breakpoints at one place are permitted, and useful if conditional.    

Do "help breakpoints" for info on other commands dealing with breakpoints.

ddd gives you a front end. I need to use it more, compare to other options

C

Library handling in linux
gcc library basics (good to know for autotools and CMake too) The gcc -l command line option specifies a specific library NAME. It will add the rest to give you (eg) lib[NAME].a Specify the library search path with the -L option. Things that you as a user install seem to default to /usr/local/lib This will link myprogram with the static library libfoo.a in the folder /home/me/foo/lib. gcc -o myprogram -lfoo -L/home/me/foo/lib myprogram.c Tools to check library dependencies: ldd [executable] objdump -p /path/to/program \| grep NEEDED objdump -x [object.so] readelf -d [exe] sudo pldd <PID> sudo pmap <PID>

Cross Compiling

C - Create a portable command line C project in Visual Studio

   Visual Studio: File -> New -> project
   Visual C++ -> Win32 -> Win32 Console Application
   name: oms_with_emap
   next -> click OFF precompiled header checkbox (even tho it didn't seem to respect it)
   you'll get a _tmain(..., TCHAR*...)
   change it to main(..., char*...)
   change the project to explicitly say "Not using precompiled header"
   remove the f'in stdafx.h
   recompile!  should be clean
   vs will recognize C files and compile accordingly

Javascript

Node.js

React

Vite

JSON

HTML

CSS

SQL

Count records within a range
This groups records into ranges, sorts by them, and gives a count, sweet: select count(*), id/1000000 as groupid from AccountHistory group by groupid;

postgres - sqlite - mysql - SQL Server - Robo 3T - DBeaver - pgadmin4

Meteor

Android

Arduino

Raspberry Pi

iOS

.NET Core

Java

Kotlin

Maven

Scala

Python

Go

PHP

php debugging
Tail these: tail -f /var/log/apache2/sitelogs/thedigitalage.org/ssl_error_log tail -f /var/log/ampache-tda/ampache.(today).log
This leads to too much noise, not needed... emacs /etc/php/apache2-php5.3/php.ini display_errors = On /etc/init.d/apache restart

Bash basics but please prefer node or python :-)

misc

SVN repo move across servers
use a tool like VisualSVN to stop SVN server copy the repo's entire svn server directory, eg: c:\svn\Software copy it into the new server under a unique name, eg: c:\svn\NewSoftware use a tool like VisualSVN to restart SVN server You should now have the new code, accessible as usual from svn. NOTE from Tom: If you move code around, make sure you tag it, then copy the tag, to preserve history (as opposed to directly moving the folder). Weird but true.

SQL Server 2008+ proper upsert using MERGE

       -- We need an "upsert": if record exists, update it, otherwise insert.
       -- There are several options to do that.
       -- Trying to do it correctly means...
       --		1) use a lock or transaction to make the upsert atomic
       --		2) use the best-available operation to maximize performance
       -- SQL Server 2008 has MERGE which may be slightly more efficient than 
       -- separate check && (insert||update) steps.  And we can do it with
       -- a single lock instead of a full transaction (which may be better?).
       -- It's messy to code up though since three blocks of fields must be specified.  
       -- Cest la vie.
       MERGE [dbo].[FACT_DCSR_RemPeriodMonthlyReport] WITH (HOLDLOCK) AS rpmr
       USING (SELECT @ID AS ID) AS new_foo
             ON rpmr.ID = new_foo.ID



               @last_months_year as DCSRYear,
               @last_month as DCSRMonth,
               @last_month_name as MonthName,
               Device_Type_ID,




       WHEN MATCHED THEN
           UPDATE
                   SET f.UpdateSpid = @@SPID, 
                   UpdateTime = SYSDATETIME() 
       WHEN NOT MATCHED THEN
           INSERT
             (
                   ID, 
                   InsertSpid, 
                   InsertTime
             )
           VALUES
             (
                   new_foo.ID, 
                   @@SPID, 
                   SYSDATETIME()
             );

Web Services

Firefox Addon development

c++ Create a portable autotools C++ project in linux
(OLD, USE CMAKE NOW) For anything serious, it's best to clone an existing project's skeleton. main.cpp MVC code nix/copy_from folder make sure .bashrc is configured for boost nix$ bootstrap_autotools_project.sh force release debug set up eclipse according to screenshots in Eclipse

c++ Create a portable C++ project in Visual Studio

(OLD, USE CMAKE NOW)

If you don't have existing code, it's probably best to create a project_name.cpp file with your main() function.

int main( int argc, char * argv[] )
{ 
    return 0;
}

Then in Visual Studio...

File->New->Project from existing code
C++
(then use mostly defaults on this page, once you provide file location and project name)
Project file location:  <base>\project_name
Project name: project_name
[x] Add files from these folders
   Add subs  
   [x]        <base>\project_name
NEXT
Use Visual Studio
  Console application project
  No ATL, MFC, CLR
NEXT
NEXT
FINISH

Then add Reusable and boost include and lib paths: Example if you built boost according to notes below:

Project->Properties->All Configurations->Configuration Properties->VC++ Directories->Include Directories->
   $(VC_IncludePath);$(WindowsSDK_IncludePath);..\..\..\Reusable\c++
INCLUDE: C:\Software Development\boost_1_53_0
LIB: C:\Software Development\boost_1_53_0\stage\lib