#define in C with curly braces

Question

I found a new form of "#define" in C but I don't understand what it means. This is source code:

#define OPT_SET_INT(s, l, v, h, i)  { OPTION_SET_INT, (s), (l), (v), NULL, \
           (h), PARSE_OPT_NOARG, NULL, (i) }

This is the definition of OPTION_SET_INT:

enum parse_opt_type {
    /* special types */
    OPTION_END,
    OPTION_ARGUMENT,
    OPTION_GROUP,
    OPTION_NUMBER,
    /* options with no arguments */
    OPTION_BIT,
    OPTION_NEGBIT,
    OPTION_COUNTUP,
    OPTION_SET_INT,
    OPTION_SET_PTR,
    OPTION_CMDMODE,
    /* options with arguments (usually) */
    OPTION_STRING,
    OPTION_INTEGER,
    OPTION_CALLBACK,
    OPTION_LOWLEVEL_CALLBACK,
    OPTION_FILENAME
};

It is in parse-option.h in this repository: https://github.com/git/git

Thanks.

Answer 1

There's nothing special about this whatsoever. Everything after the macro name (and parenthesis) gets plopped in-place verbatim, with the exception of the macro parameters, which are replaced.

In this case, the macro is used to populate one entry in an array of struct option .

Eg In some C file you might have:

 struct option options[] = {
    OPT_SET_INT(foo, bar, snap, crackle, pop),
    OPT_SET_INT(somethingelse, runningout, offake, names, forthis),
 };

which becomes:

 struct option options[] = {
     { OPTION_SET_INT, foo, bar, snap, NULL, crackle, PARSE_OPT_NOARG, NULL, pop },
     { OPTION_SET_INT, somethingelse, runningout, offake, NULL, names, PARSE_OPT_NOARG, NULL, forthis},
 };

(note the \\ in the macro definition is escaping the newline, so that the definition can span multiple lines).

See GCC Macro Expansion for more information.