Defer cleanup for C (gcc and llvm)

defer.h

#define DEFER_MERGE(a,b) a##b
#define DEFER_VARNAME(a) DEFER_MERGE(defer_scopevar_, a)
#define DEFER_FUNCNAME(a) DEFER_MERGE(defer_scopefunc_, a)
#define DEFER(BLOCK) void DEFER_FUNCNAME(__LINE__)(int *a) BLOCK; __attribute__((cleanup(DEFER_FUNCNAME(__LINE__)))) int DEFER_VARNAME(__LINE__)

// Usage:
/*
  void dosomething()
  {
    char* data = malloc(100);
    DEFER({ free(data); });
    
    dosomethingwith(data);
  }
*/

Try this https://godbolt.org/z/6Y8Ys4dPo

Any C version and any compiler.

Nice! You can add __attribute__((unused)) before the int *a parameter to get rid of the unused-parameter warning:

...
#define DEFER(BLOCK) void DEFER_FUNCNAME(__LINE__)(__attribute__((unused)) int *a) BLOCK; __attribute__((cleanup(DEFER_FUNCNAME(__LINE__)))) int DEFER_VARNAME(__LINE__)

Now simpler to re-use: https://godbolt.org/z/zsYre5Kfj

@sinecode
Did you manage to get rid of the warning: ISO C forbids nested functions [-Wpedantic] warning?