Question

有没有办法防止C中的缓冲区溢出？如果我无法确定字符串长度，我怎么知道何时停止？

x = malloc(strlen(unsafe_string) + 1);
memcpy(x, unsafe_string, strlen(unsafe_string) + 1);

Answer 1

使用strnlen并检查malloc是否成功，如此

#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[]) {
  char *unsafe_string = "hello, world"; /* whatever */

  size_t max_len = 1024 * 1024; /* one megabyte */
  size_t len = strnlen(unsafe_string, max_len) + 1; /* the smaller of the length, 
                                                       or 1 mb */
  char *x = malloc(len * sizeof(char *)); /* malloc len */
  if (x != NULL) { /* check for success */
    strncpy(x, unsafe_string, len); /* safe string copy */
    x[len+1] = '\0';
    puts(x);
    free(x);
  }
}

只打印

$ gcc hello.c
$ ./a.out 
hello, world

这里。

防止C中的缓冲区溢出

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