C语言#与##最直白的用法介绍

假设你需要封装如下接口：

cpp 复制代码

int32_t display_set_hdr_type(const dispmng_display_id id, int32_t value);
int32_t display_set_hdr_match_content(const dispmng_display_id id, int32_t value);
int32_t display_set_hdr_quality(const dispmng_display_id id, int32_t value);

他们的函数实现都非常类似。感觉写起来有许多重复的代码。那么你可以用如下的方式写：

cpp 复制代码

#define display_set_hdr(name, id, para_type, value)  \
int32_t display_set_hdr_##name(const dispmng_display_id id, int32_t value){\
    int32_t ret = -1;\
    LOGI("display_set_hdr_%s id=%d, value=%d", #name, id, value);\
    do {\
        uapi_ret_if_invalid_id(id);\
        ret = uapi_svr_dispmng_init();\
        if (ret != SUCCESS) {\
            LOGD("uapi_svr_dispmng_init() failed: %d", ret);\
            break;\
        }\
        ret = uapi_svr_dispmng_set_hdr_##name(id, (para_type)value);\
        uapi_svr_dispmng_deinit();\
    } while(0);\
    return ret;\
}


display_set_hdr(type, id, uapi_svr_dispmng_hdr_type, value)
display_set_hdr(match_content, id, bool, value)
display_set_hdr(quality, id, int32_t, value)

宏展开看一下 gcc -E macro.c -o macro.i

cpp 复制代码

# 0 "macro.c"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "macro.c"
# 22 "macro.c"
int32_t display_set_hdr_type(const dispmng_display_id id, int32_t value){ int32_t ret = -1; LOGI("display_set_hdr_%s id=%d, value=%d", "type", id, value); do { uapi_ret_if_invalid_id(id); ret = uapi_svr_dispmng_init(); if (ret != SUCCESS) { LOGD("uapi_svr_dispmng_init() failed: %d", ret); break; } ret = uapi_svr_dispmng_set_hdr_type(id, (uapi_svr_dispmng_hdr_type)value); uapi_svr_dispmng_deinit(); } while(0); return ret;}
int32_t display_set_hdr_match_content(const dispmng_display_id id, int32_t value){ int32_t ret = -1; LOGI("display_set_hdr_%s id=%d, value=%d", "match_content", id, value); do { uapi_ret_if_invalid_id(id); ret = uapi_svr_dispmng_init(); if (ret != SUCCESS) { LOGD("uapi_svr_dispmng_init() failed: %d", ret); break; } ret = uapi_svr_dispmng_set_hdr_match_content(id, (bool)value); uapi_svr_dispmng_deinit(); } while(0); return ret;}
int32_t display_set_hdr_quality(const dispmng_display_id id, int32_t value){ int32_t ret = -1; LOGI("display_set_hdr_%s id=%d, value=%d", "quality", id, value); do { uapi_ret_if_invalid_id(id); ret = uapi_svr_dispmng_init(); if (ret != SUCCESS) { LOGD("uapi_svr_dispmng_init() failed: %d", ret); break; } ret = uapi_svr_dispmng_set_hdr_quality(id, (int32_t)value); uapi_svr_dispmng_deinit(); } while(0); return ret;}

是不是觉得#跟##用起来很清爽了？