C-Programming Structures

[ZED0815]

Hi Guys,

here is a question for you:

It is possible to define a structure like

struct test {
   int a;
   int b;
};

and create an instance of it:

struct test mytest;
mytest.a = 1;
mytest.b = 22;

Or, create an instance and initialize it at the same time:

struct test mytest = { 1, 22 };

Now, is it possible to use Method B, initializing just a bunch of members in a random sequence (example given doesn't work - just for illustration what I mean...)???

struct test mytest = { b = 22 }; //which fails since b is not defined here...
struct test mytest2 = { b = 22, a = 1 };

Thanks for your advice!

Best,

Axel

[Catfish3]

You can, in C (C99). And it would look very similar to your code:

struct test mytest = { .b = 22, .a = 1 };

Edit: while C++ does not "officially" support designated initializers, certain C++ compilers may let you do this, I'm thinking about GCC.

Edit 2: added a for completeness.

[ZED0815]

Thanks for your quick answer, Catfish3!

[Catfish3]

Tested this on GCC 4.8.0. Works fine with a warning:

designated_initializer.cpp: In function 'int main()':
designated_initializer.cpp:11:14: warning: ISO C++ does not allow C99 designated initializers [-Wpedantic]
     Test t = {.i = 1, .c = 'a'};
              ^
designated_initializer.cpp:11:21: warning: ISO C++ does not allow C99 designated initializers [-Wpedantic]
     Test t = {.i = 1, .c = 'a'};
                     ^

1 2 3 4 5 6 7 8 9 10 11 12 13 14

#include <iostream> struct Test { int i; char c; }; int main() { Test t = {.i = 1, .c = 'a'}; std::clog << "t.i == " << t.i << '\t' << "t.c == " << t.c << '\n'; }

t.i == 1 t.c == a