将 va_list 转换为变量参数? [英] converting va_list to variable argument?

问题描述

我有一个函数 log_message 它接受可变参数.

I have a function log_message it takes variable arguments.

log_message(int level, char *fmt, ...)

现在在调用这个(log_message) 函数之前，我必须添加新函数(_log_message)，新函数将调用log_message.

now before calling this(log_message) function i have to add new function(_log_message), and new function will call log_message.

_log_message(int level, char *fmt, ...)

新功能也一样.当_log_message 调用log_message 时，它会将变量输入转换为va_list.现在我有了va_list，我不想改变原来的，有什么办法可以改回变量输入，这样我就可以调用原来的(log_message).

new function is also same. when _log_message will call log_message it will convert variable input to va_list. Now i have va_list, i don't wanna change the original one, is there any way to change back to variable input, so i will able to call the original one(log_message).

推荐答案

不，没有办法将 va_list 转换回参数列表.

No, there is no way to turn a va_list back into a list of arguments.

通常的方法是定义一个以 va_list 作为参数的基本函数.例如，标准C库定义了printf和vprintf；第一个是可变参数函数，第二个具有完全相同的功能，但使用 va_list 代替.同样，它定义了fprintf 和vfprintf.用vfprintf来定义printf、vprintf和fprintf很简单:

The usual approach is to define a base function which takes a va_list as an argument. For example, the standard C library defines printf and vprintf; the first is a varargs function and the second has exactly the same functionality but takes a va_list instead. Similarly, it defines fprintf and vfprintf. It's trivial to define printf, vprintf and fprintf in terms of vfprintf:

int fprintf(FILE* stream, const char* format, ...) {
  va_list ap;
  va_start(ap, format);
  int n = vfprintf(stream, format, ap);
  va_end(ap);
  return n;
}

int vprintf(const char* format, va_list ap) {
  return vfprintf(stdout, format, ap);
}

int printf(const char* format, ...) {
  va_list ap;
  va_start(ap, format);
  int n = vprintf(format, ap);
  va_end(ap);
  return n;
}

(类似于各种 exec* 函数，它们有 va_list 和 varargs 两种.)

(Similarly for the various exec* functions, which come in both va_list and varargs varieties.)

我建议您采用类似的策略.

I'd suggest you adopt a similar strategy.

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