oc字符串与c字符串转换和拷贝

// Helper method to create C string copy
NSString* MakeNSString (const char* string) {
    if (string) {
        return [NSString stringWithUTF8String: string];
    } else {
        return [NSString stringWithUTF8String: ""];
    }
}

char* MakeCString(NSString *str) {
    const char* string = [str UTF8String];
    if (string == NULL) {
        return NULL;
    }

    char* res = (char*)malloc(strlen(string) + );
    strcpy(res, string);
    return res;
}