What's wrong with strndup?

问题

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?

回答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.

回答2:

strndup is a GNU extension and is not present on Mac OS X. You will have to either not use it or supply some implementation, like this one.

回答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;
}

来源：https://stackoverflow.com/questions/6062822/whats-wrong-with-strndup