无法使用Printf!？! (使用 mhash 执行哈希算法时)

Question

我正在使用 Mhash，我想打印 block 大小的长度以用于调试目的，但每次尝试编译时我都会收到错误

关于如何修复此错误有什么建议吗？

这是我的代码:

#include <mhash.h>
#include <stdio.h>
#include <string.h>

// 0x12e6bc6e68c3b9506e6668db6b7224f894fab073728fc179 (TIGER192) (48)

 int main()
 {
        char password[] = "Jefe";
        int keylen = 4; 
        char data[] = "what do ya want for nothing?";
        int datalen = 28;
        MHASH td, td2;
        unsigned char *mac, *mac2;
        int i, j;

    td = mhash_hmac_init(MHASH_TIGER192, password, keylen, mhash_get_hash_pblock(MHASH_TIGER192));

        mhash(td, data, datalen); 
        mac = mhash_hmac_end(td); 

        printf("0x");
        for (i = 0; i < mhash_get_block_size(MHASH_TIGER192); i++)
    {
                printf("%.2x", mac[i]);
        }
        printf("\n");

    // int length = strlen(mac);
    // printf(length);

    // int length = 5;
    // printf(length);

        exit(0);
 }

I run the program with the following commands:
hb2@hb1:~/Desktop$ gcc -o hashexample hashexample.c -lmhash
hb2@hb1:~/Desktop$ ./hashexample
0x12e6bc6e68c3b9506e6668db6b7224f894fab073728fc179

它运行成功，但是当我尝试打印哈希结果的长度时，出现以下错误!!？关于原因有什么想法吗？

// int length = strlen(mac);
// printf(length);

hb2@hb1:~/Desktop$ gcc -o hashexample hashexample.c -lmhash
hashexample.c: In function ‘main’:
hashexample.c:33:2: warning: passing argument 1 of ‘printf’ makes pointer from integer without a cast [enabled by default]
/usr/include/stdio.h:363:12: note: expected ‘const char * __restrict__’ but argument is of type ‘int’
hashexample.c:33:2: warning: format not a string literal and no format arguments [-Wformat-security]

一开始我以为是因为我以为我使用了strlen错误？!但即使当我尝试对整数执行简单的 printf 时，我仍然收到错误:

// int length = 5;
// printf(length);

hb2@hb1:~/Desktop$ gcc -o hashexample hashexample.c -lmhash
hashexample.c: In function ‘main’:
hashexample.c:35:2: warning: passing argument 1 of ‘printf’ makes pointer from integer without a cast [enabled by default]
/usr/include/stdio.h:363:12: note: expected ‘const char * __restrict__’ but argument is of type ‘int’
hashexample.c:35:2: warning: format not a string literal and no format arguments [-Wformat-security]

提前感谢您的帮助!

Answer 1

检查man page for printf() 。第一个参数是 const char * 。您正在传递 int .

警告也是如此:

warning: passing argument 1 of ‘printf’ makes pointer from integer without a cast [enabled by default]

你想要:

printf("%d", length);

您需要格式字符串来指定 int即将打印。