strdup NSString to C string

StrdupNS.m

#import <Foundation/Foundation.h>
#include <stdlib.h>
static inline char* strdupNS(NSString* nss) {
    static const NSStringEncoding enc = NSUTF8StringEncoding;
    NSUInteger len = [nss lengthOfBytesUsingEncoding:enc];
    if (len <= 0) {
        return NULL;
    }
    char* cstr = malloc((size_t)(1 + len));
    if (![nss getCString:cstr maxLength:(1 + len) encoding:enc]) {
        free(cstr);
        return NULL;
    }
    return cstr;
}