变参函数加打印

[xie6723632]

假设有一个在库里的无法看到源码的变参函数int func(int a,...);如何实现一个函数或者宏实现类似以下功能。

int printf_func(int a,...)
{
printf("the first parameter is %d\n",a);
return func(a,...);
}
可以用宏实现，但是要确保
printf_func(a,...);和if(printf_func(a,...)<0)这种都能正常展开。
多谢了。

[赵4老师]

Calls with a Variable Number of Arguments A partial parameter list can be terminated by the ellipsis notation, a comma followed by three periods (, ...), to indicate that there may be more arguments passed to the function, but no more information is given about them. Type checking is not performed on such arguments. At least one parameter must precede the ellipsis notation and the ellipsis notation must be the last token in the parameter list. Without the ellipsis notation, the behavior of a function is undefined if it receives parameters in addition to those declared in the parameter list. To call a function with a variable number of arguments, simply specify any number of arguments in the function call. An example is the printf function from the C run-time library. The function call must include one argument for each type name declared in the parameter list or the list of argument types. All the arguments specified in the function call are placed on the stack unless the __fastcall calling convention is specified. The number of parameters declared for the function determines how many of the arguments are taken from the stack and assigned to the parameters. You are responsible for retrieving any additional arguments from the stack and for determining how many arguments are present. The STDARGS.H file contains ANSI-style macros for accessing arguments of functions which take a variable number of arguments. Also, the XENIX®- style macros in VARARGS.H are still supported. This sample declaration is for a function that calls a variable number of arguments: int average( int first, ...); Microsoft Specific —> To maintain compatibility with previous versions of Microsoft C, a Microsoft extension to the ANSI C standard allows a comma without trailing periods (,) at the end of the list of parameters to indicate a variable number of arguments. However, it is recommended that code be changed to incorporate the ellipsis notation. END Microsoft Specific

[幻夢之葉]

试试

int printf_func(int a, ...)
{
    va_list args;
    va_start(args, a);
    func(a, args);
    va_end(args);
}

[LubinLew]

#define printf_func(a, ...)  (printf("the first parameter is %d\n",a), func(a, ##__VA_ARGS__))

[paschen]

http://www.cnblogs.com/caosiyang/archive/2012/08/21/2648870.html