strndup有什么问题？

Question

I'm writing a parser using flex. I'm using Mac OS X 10.6.7. I have already include header files like this:

#include "string.h"
#include "stdlib.h"

but it says

Undefined symbols for architecture x86_64:
  "_strndup", referenced from:
      _yylex in ccl2332A.o
ld: symbol(s) not found for architecture x86_64

why?

Answer 1

AFAIK there is no method strndup in string.h or stdlib.h, try using strdup() which is probably what you want. If you really need to specifiy the length you want allocated you could do it using malloc and memcpy instead.

Answer 2

strndup是一个GNU扩展，在Mac OS X上不存在。你必须要么不使用它，要么提供一些实现，比如这个 。

Answer 3

If you need a strndup implementation, you can use this one.

char *strndup(char *str, int chars)
{
    char *buffer;
    int n;

    buffer = (char *) malloc(chars +1);
    if (buffer)
    {
        for (n = 0; ((n < chars) && (str[n] != 0)) ; n++) buffer[n] = str[n];
        buffer[n] = 0;
    }

    return buffer;
}