c - va_copy() 是否需要 va_end()？

Question

在处理可变参数时，是只是 va_start() 需要匹配的 va_end() 调用，还是 va_copy()也需要匹配的 va_end()，即

void foo(char *x, ...)
{
  va_list l,c;

  va_start(l,x);
  va_copy(c,l);

  ---
  va_end(c); //is this correct ?
  va_end(l);
}

Answer 1

是的，每个副本和原件都需要调用 va_end()。您的示例是正确的，您的 va_end() 调用顺序可以颠倒。

来自 ISO/IEC 9899:201x:

7.16.1.3 The va_end macro

The va_end macro facilitates a normal return from the function whose variable argument list was referred to by the expansion of the va_start macro, or the function containing the expansion of the va_copy macro, that initialized the va_list ap. The va_end macro may modify ap so that it is no longer usable (without being reinitialized by the va_start or va_copy macro). If there is no corresponding invocation of the va_start or va_copy macro, or if the va_end macro is not invoked before the return, the behavior is undefined.

最后一句指出每个 va_start 或 va_copy 在返回之前必须伴随一个 va_end。