小编pen*_* xu的帖子

例如,我看到像流动的源代码.我们可以#define在一个函数中使用吗？它是如何工作的？(更多信息:这些代码是我从openvswitch源代码中复制的代码):

void *
ofputil_put_action(enum ofputil_action_code code, struct ofpbuf *buf)
{
switch (code) {
case OFPUTIL_ACTION_INVALID:

#define OFPAT13_ACTION(ENUM, STRUCT, EXTENSIBLE, NAME) case OFPUTIL_##ENUM:
#include "ofp-util.def"
    OVS_NOT_REACHED();

#define OFPAT10_ACTION(ENUM, STRUCT, NAME)                  \
case OFPUTIL_##ENUM: return ofputil_put_##ENUM(buf);
#define OFPAT11_ACTION(ENUM, STRUCT, EXTENSIBLE, NAME)      \
case OFPUTIL_##ENUM: return ofputil_put_##ENUM(buf);
#define NXAST_ACTION(ENUM, STRUCT, EXTENSIBLE, NAME)        \
case OFPUTIL_##ENUM: return ofputil_put_##ENUM(buf);
#include "ofp-util.def"
}
OVS_NOT_REACHED();
}

#define OFPAT10_ACTION(ENUM, STRUCT, NAME)                        \
void                                                        \
ofputil_init_##ENUM(struct STRUCT *s)                       \
{                                                           \
    memset(s, 0, sizeof *s); …

例如,我将AA定义三次,是否合法？:

#include<stdio.h>
#define AA 10
#define AA 20
#define AA 30
int main() {
    printf("AA");
}