使用 snprintf 避免缓冲区溢出 [英] Using snprintf to avoid buffer overruns

问题描述

我像这样使用 snprintf 来避免缓冲区溢出:

I am using snprintf like this to avoid a buffer overrun:

char err_msg[32] = {0};
snprintf(err_msg, sizeof(err_msg) - 1, "[ ST_ENGINE_FAILED ]");

我添加了 -1 来为空终止符保留空间，以防字符串长度超过 32 个字节.

I added the -1 to reserve space for the null terminator in case the string is more than 32 bytes long.

我的想法是否正确?

平台:

• 海湾合作委员会 4.4.1
• C99

推荐答案

正如其他人所说，在这种情况下您不需要 -1.如果数组是固定大小，我会使用 strncpy 代替.它用于复制字符串 - sprintf 用于处理困难的格式化.但是，如果数组的大小未知，或者您正在尝试确定格式化字符串需要多少存储空间.这就是我真正喜欢 snprintf 的标准指定版本的地方:

As others have said, you do not need the -1 in this case. If the array is fixed size, I would use strncpy instead. It was made for copying strings - sprintf was made for doing difficult formatting. However, if the size of the array is unknown or you are trying to determine how much storage is necessary for a formatted string. This is what I really like about the Standard specified version of snprintf:

char* get_error_message(char const *msg) {
    size_t needed = snprintf(NULL, 0, "%s: %s (%d)", msg, strerror(errno), errno);
    char  *buffer = malloc(needed+1);
    sprintf(buffer, "%s: %s (%d)", msg, strerror(errno), errno);
    return buffer;
}

将此功能与 va_copy 结合使用，您可以创建非常安全的格式化字符串操作. 

Combine this feature with va_copy and you can create very safe formatted string operations.  

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