c - c 中具有常量参数的结构体数组

Question

我定义了以下结构

typedef const struct _txmlAttribute
{
 const char * const ns;
} txmlAttribute;

在下面的函数中我想初始化我的结构的动态数组:

int func(txmlAttribute* attrs){
    attrs = (txmlAttribute*) { {"as"}, {"bs"}};
    return 0;
}

int main(){
   txmlAttribute* attrs;
   func(attrs);
   return 0; 
}

但我收到这些警告:

main.c: In function ‘func’:
main.c:13:5: warning: braces around scalar initializer [enabled by default]
     attrs = (txmlAttribute*) { {"as"}, {"bs"}};
 ^
main.c:13:5: warning: (near initialization for ‘(anonymous)’) [enabled by default]
main.c:13:5: warning: initialization from incompatible pointer type [enabled by default]
main.c:13:5: warning: (near initialization for ‘(anonymous)’) [enabled by default]
main.c:13:5: warning: braces around scalar initializer [enabled by default]
main.c:13:5: warning: (near initialization for ‘(anonymous)’) [enabled by default]
main.c:13:5: warning: initialization from incompatible pointer type [enabled by default]
main.c:13:5: warning: (near initialization for ‘(anonymous)’) [enabled by default]
main.c:13:5: warning: excess elements in scalar initializer [enabled by default]
main.c:13:5: warning: (near initialization for ‘(anonymous)’) [enabled by default]

那么这是为什么呢？我怎样才能清除它？

Answer 1

您的问题是 {{"as"}, {"bs"}} 将在堆栈上分配，并且在您离开函数范围后将变得无效*。

我会通过编写一个“构造函数”函数来实现这一点，该函数将字段作为参数，为结构及其成员分配(malloc)所需的空间，初始化它们并返回指向该结构的指针。那么填充数组的代码将类似于:

txmlAttribute attrs[2];
attrs[0] = make_txml_attr("as");
attrs[1] = make_txml_attr("bs");

txmlAttribute * make_txml_attr(const char * val) {
  txmlAttribute * res = malloc(sizeof(txmlAttribute));   
  res->ns = strdup(val);
  return res;
}


void free_txml_attr(const char ** p_attr) {
   free(*p_attr->ns);
   free(*p_attr);
   *p_attr = NULL;
}

(我省略了错误检查)

--

无效 - 因为访问它将是未定义的行为