c - 如何检查宏是否可用

Question

我试图查看我的 libcurl 是否支持 CURLSSLBACKEND_OPENSSL，但迷路了。如何判断是否设置了宏？完成此任务的正确方法是什么？

代码如下:

#include <stdio.h>
#include <curl/curl.h>

int main(){
        printf("CURLSSLBACKEND_OPENSSL is %d\n", CURLSSLBACKEND_OPENSSL);

#if (CURLSSLBACKEND_OPENSSL == 1)
        puts("CURLSSLBACKEND_OPENSSL is 1");
#else
        puts("CURLSSLBACKEND_OPENSSL is NOT 1");
#endif

#ifndef CURLSSLBACKEND_OPENSSL
        #define CURLSSLBACKEND_OPENSSL 0
#endif
        printf("CURLSSLBACKEND_OPENSSL is %d\n", CURLSSLBACKEND_OPENSSL);


#ifdef meh
        printf("meh is defined!\n");
#else
        printf("meh is NOT defined!\n");
#endif
        return 0;
}

这是输出，它是错误的:

 $ ./a.out
CURLSSLBACKEND_OPENSSL is 1
CURLSSLBACKEND_OPENSSL is NOT 1 // <-- wrong
CURLSSLBACKEND_OPENSSL is 0     // <-- nope..
meh is NOT defined!

任何建议将不胜感激，提前致谢!

Answer 1

感谢您的指点，给我发了right方式。

我的代码已修改如下:

curl_version_info_data  *curl_version_data;
+#if LIBCURL_VERSION_NUM >= 0x073800
+        if (curl_version_data->version_num >= 0x073800){
+                printf("Setting CURLSSLBACKEND_OPENSSL\n");
+                CURLsslset result;
+                result = curl_global_sslset((curl_sslbackend)1, NULL, NULL);
+                assert(result == CURLSSLSET_OK);
+        } else {
+                printf("libcurl version too old to set CURLSSLBACKEND_OPENSSL\n");
+        }
+#else
+#warning "libcurl version too old to set CURLSSLBACKEND_OPENSSL"
+               printf("libcurl version too old to set CURLSSLBACKEND_OPENSSL\n");
+#endif
+
+

它似乎正在做我最初的意图。