博客內容參考自 cplusplus
頭文件解釋
頭文件名字:stdarg
英文原文解釋:
Variable arguments handling
This header defines macros to access the individual arguments of a list of unnamed arguments whose number and types are not known to the called function.A function may accept a varying number of additional arguments without corresponding parameter declarations by including a comma and three dots (,...) after its regular named parameters:
return_type function_name ( parameter_declarations , ... );
To access these additional arguments the macros va_start, va_arg and va_end, declared in this header, can be used:
- First, va_start initializes the list of variable arguments as a va_list.
- Subsequent executions of va_arg yield the values of the additional arguments in the same order as passed to the function.
- Finally, va_end shall be executed before the function returns.
個人理解:
C/C++裏面存在一種機制,可以使得函數可以接受可變參數,可變參數的意思是變量參數名未知、變量參數類型未知、變量參數數量未知。
函數聲明方式是,第一個參數是一個符合語法的確定的參數,後接一個逗號以及三個英文符號的點(省略號)
return_type function_name ( parameter_declarations, ... );
使用方法
類型 va_list 定義用於接受可變參數的變量,然後通過 void va_start(va_list ap, paramN) 函數來初始化加下來的N個未知參數
然後通過 type va_arg(va_list ap, type) 函數來獲取ap中的未知參數
在函數返回前要調用 void va_end(va_list ap) 函數來取回
可以通過 int vsprintf(char *s, const char *format, va_list ap); 函數來實現一種特殊用法,下面源碼有具體的思想方法
實例
/* vsprintf example */
#include <stdio.h>
#include <stdarg.h>
void PrintFError ( const char * format, ... )
{
char buffer[256];
va_list args;
va_start (args, format);
vsprintf (buffer,format, args);
perror (buffer);
va_end (args);
}
int main ()
{
FILE * pFile;
char szFileName[]="myfile.txt";
pFile = fopen (szFileName,"r");
if (pFile == NULL)
PrintFError ("Error opening '%s'",szFileName);
else
{
// file successfully open
fclose (pFile);
}
return 0;
}
* 具體情況可直接去cplusplus網站學習