Recently, I found myself kind of annoyed by the fact that I couldn’t use the same “initialization” syntax to directly set the values of an existing structure. Extremely trivial, but it bugs me. Is there really a good reason for this limitation?
typedef struct
{
int x;
int y;
} Doh;
Doh doh = { 1, 2 };
// You can't directly re-assign in one step, bummer.
// doh = { 3, 4 };
// You need a second struct to use the same syntax. Yuck.
Doh d2 = { 3, 4 };
doh = d2;
// Or just do it longhand. Also yuck.
doh.x = 5;
doh.y = 6;
So I dug around to see if there was anything I was missing, and I found designated initializers, the new initialization method available in C99. It doesn’t allow me to directly assign values to an existing structure, but it is interesting:
Doh doh_set = {
.x = 4,
.y = 3
};
Doh doh_set2 = {
.y = 3,
.x = 4
};
Doh doh_set3 = {
.y = 3
};
Doh set4[]=
{
{
.y = 1039
},
{
.y = 1040,
.x = 23
}
};
Still not rocket science, but the truly interesting part is that designated initializers are not yet available in C++. At least not today. I tested it with gcc 4.1.2 and Visual Studio 2008 C++ compilers and they do not support it. It may appear in C++0x, but for now, C is definitely no longer a pure subset of C++. For more possible gotchas (and some C99 features that make it more compatible with C++), here’s a quick C99 rundown.
Considering designated initializers are being used in places like the linux kernel, this issue no longer seems trivial. Oh well, code and learn. Hopefully I can go another 10 years(!) before my next snag. For now, back to classes… :>
