va_list和va_start的使用

[wujingyi2011]

#include <stdio.h>

void main()
{
TestFun("sssssssssss",5,"s");
}

void TestFun(char* pszDest, int DestLen, const char* pszFormat, ...)
{
va_list args;
va_start(args, pszFormat);
_vsnprintf(pszDest, DestLen, pszFormat, args);
va_end(args);
}

请教怎么写才是对的呢？

[漫步者、]

#include <stdio.h>
#define ANSI            /* Comment out for UNIX version     */
#ifdef ANSI             /* ANSI compatible version          */
#include <stdarg.h>
int average( int first, ... );
#else                   /* UNIX compatible version          */
#include <varargs.h>
int average( va_list );
#endif

void main( void )
{
   /* Call with 3 integers (-1 is used as terminator). */
   printf( "Average is: %d\n", average( 2, 3, 4, -1 ) );

   /* Call with 4 integers. */
   printf( "Average is: %d\n", average( 5, 7, 9, 11, -1 ) );

   /* Call with just -1 terminator. */
   printf( "Average is: %d\n", average( -1 ) );
}

/* Returns the average of a variable list of integers. */
#ifdef ANSI             /* ANSI compatible version    */
int average( int first, ... )
{
   int count = 0, sum = 0, i = first;
   va_list marker;

   va_start( marker, first );     /* Initialize variable arguments. */
   while( i != -1 )
   {
      sum += i;
      count++;
      i = va_arg( marker, int);
   }
   va_end( marker );              /* Reset variable arguments.      */
   return( sum ? (sum / count) : 0 );
}
#else       /* UNIX compatible version must use old-style definition.  */
int average( va_alist )
va_dcl
{
   int i, count, sum;
   va_list marker;

   va_start( marker );            /* Initialize variable arguments. */
   for( sum = count = 0; (i = va_arg( marker, int)) != -1; count++ )
      sum += i;
   va_end( marker );              /* Reset variable arguments.      */
   return( sum ? (sum / count) : 0 );
}
#endif

[AnYidan]

google, 看看别人如何写的

[namelcz]

这个是要实现参数不确定个数的吧！

[清钟沁桐]

加头文件 #include <stdarg.h>

#include <stdio.h>
#include <stdarg.h>


void TestFun(char* pszDest, int DestLen, const char* pszFormat, ...)
{
    va_list args;
    va_start(args, pszFormat);
    _vsnprintf(pszDest, DestLen, pszFormat, args);
    va_end(args);
}

void main()
{
    char temp[128];
    TestFun("sssssssssss",5,"s");
}

[nadleeh]

引用 楼主 wujingyi2011 的回复:

#include <stdio.h> void main() { TestFun("sssssssssss",5,"s"); } void TestFun(char* pszDest, int DestLen, const char* pszFormat, ...) { va_list args; va_start(args, pszForma……

变长参数提供的标准宏

[craboy1]

#include <stdio.h>
#include <stdarg.h>
#include <malloc.h>

void test(const char *fmt, ...);
int my_printf();

int main(void)
{
        test("%s %d %s","test",10,"hello world");
        return 0;
}


void
test(const char *fmt, ...)
{
        va_list ap;
        va_start(ap, fmt);
        my_printf(fmt, ap);
        va_end(ap);
}

int my_printf(const char *fmt, va_list ap){
        char buf[1024];
        size_t len;
        len = sizeof(buf);
        int r = vsnprintf(buf, len, fmt, ap);
        buf[len-1] = '\0';
        printf("%s\n",buf);
        return r;
}

[wujingyi2011]

#include <stdio.h>
#include <stdarg.h>

void TestFun(char* pszDest, int DestLen, const char* pszFormat, ...)
{
va_list args;
va_start(args, pszFormat);
_vsnprintf(pszDest, DestLen, pszFormat, args);
va_end(args);
}

void main()
{
//char temp[128];
TestFun("sssssssssss",5,"s");
}
运行弹出错误提示窗口

[zslInSz]

引用 7 楼 wujingyi2011 的回复:

#include <stdio.h> #include <stdarg.h> void TestFun(char* pszDest, int DestLen, const char* pszFormat, ...) { va_list args; va_start(args, pszFormat); _vsnprintf(pszDe……

你的函数调用不对，第一个参数不能够传递“sssssss”，应该传递的和sprintf第一个参数一样的，带有格式化的字符串

[wujingyi2011]

#include <stdio.h> #include <stdarg.h> void TestFun(char* pszDest, int DestLen, const char* pszFormat, ...) { va_list args; va_start(args, pszFormat); _vsnprintf(pszDest, DestLen, pszFormat, args); va_end(args); } void main() { char s[10]="sssssssss"; TestFun(s,5,"s"); }

[赵4老师]

查MSDN是Windows程序员必须掌握的技能之一。 mk:@MSITStore:C:\MSDN98\98VS\2052\vccore.chm::/html/_crt_va_arg.2c_.va_end.2c_.va_start.htm va_arg, va_end, va_start Access variable-argument lists. type va_arg( va_list arg_ptr, type ); void va_end( va_list arg_ptr ); void va_start( va_list arg_ptr ); (UNIX version) void va_start( va_list arg_ptr, prev_param ); (ANSI version) Routine Required Header Optional Headers Compatibility va_arg <stdio.h> and <stdarg.h> <varargs.h>1 ANSI, Win 95, Win NT va_end <stdio.h> and <stdarg.h> <varargs.h>1 ANSI, Win 95, Win NT va_start <stdio.h> and <stdarg.h> <varargs.h>1 ANSI, Win 95, Win NT 1 Required for UNIX V compatibility. For additional compatibility information, see Compatibility in the Introduction. Libraries LIBC.LIB Single thread static library, retail version LIBCMT.LIB Multithread static library, retail version MSVCRT.LIB Import library for MSVCRT.DLL, retail version Return Value va_arg returns the current argument; va_start and va_end do not return values. Parameters type Type of argument to be retrieved arg_ptr Pointer to list of arguments prev_param Parameter preceding first optional argument (ANSI only) Remarks The va_arg, va_end, and va_start macros provide a portable way to access the arguments to a function when the function takes a variable number of arguments. Two versions of the macros are available: The macros defined in STDARG.H conform to the ANSI C standard, and the macros defined in VARARGS.H are compatible with the UNIX System V definition. The macros are: va_alist Name of parameter to called function (UNIX version only) va_arg Macro to retrieve current argument va_dcl Declaration of va_alist (UNIX version only) va_end Macro to reset arg_ptr va_list typedef for pointer to list of arguments defined in STDIO.H va_start Macro to set arg_ptr to beginning of list of optional arguments (UNIX version only) Both versions of the macros assume that the function takes a fixed number of required arguments, followed by a variable number of optional arguments. The required arguments are declared as ordinary parameters to the function and can be accessed through the parameter names. The optional arguments are accessed through the macros in STDARG.H or VARARGS.H, which set a pointer to the first optional argument in the argument list, retrieve arguments from the list, and reset the pointer when argument processing is completed. The ANSI C standard macros, defined in STDARG.H, are used as follows: All required arguments to the function are declared as parameters in the usual way. va_dcl is not used with the STDARG.H macros. va_start sets arg_ptr to the first optional argument in the list of arguments passed to the function. The argument arg_ptr must have va_list type. The argument prev_param is the name of the required parameter immediately preceding the first optional argument in the argument list. If prev_param is declared with the register storage class, the macro’s behavior is undefined. va_start must be used before va_arg is used for the first time. va_arg retrieves a value of type from the location given by arg_ptr and increments arg_ptr to point to the next argument in the list, using the size of type to determine where the next argument starts. va_arg can be used any number of times within the function to retrieve arguments from the list. After all arguments have been retrieved, va_end resets the pointer to NULL. The UNIX System V macros, defined in VARARGS.H, operate somewhat differently: Any required arguments to the function can be declared as parameters in the usual way. The last (or only) parameter to the function represents the list of optional arguments. This parameter must be named va_alist (not to be confused with va_list, which is defined as the type of va_alist). va_dcl appears after the function definition and before the opening left brace of the function. This macro is defined as a complete declaration of the va_alist parameter, including the terminating semicolon; therefore, no semicolon should follow va_dcl. Within the function, va_start sets arg_ptr to the beginning of the list of optional arguments passed to the function. va_start must be used before va_arg is used for the first time. The argument arg_ptr must have va_list type. va_arg retrieves a value of type from the location given by arg_ptr and increments arg_ptr to point to the next argument in the list, using the size of type to determine where the next argument starts. va_arg can be used any number of times within the function to retrieve the arguments from the list. After all arguments have been retrieved, va_end resets the pointer to NULL. Example /* VA.C: The program below illustrates passing a variable * number of arguments using the following macros: * va_start va_arg va_end * va_list va_dcl (UNIX only) */ #include <stdio.h> #define ANSI /* Comment out for UNIX version */ #ifdef ANSI /* ANSI compatible version */ #include <stdarg.h> int average( int first, ... ); #else /* UNIX compatible version */ #include <varargs.h> int average( va_list ); #endif void main( void ) { /* Call with 3 integers (-1 is used as terminator). */ printf( "Average is: %d\n", average( 2, 3, 4, -1 ) ); /* Call with 4 integers. */ printf( "Average is: %d\n", average( 5, 7, 9, 11, -1 ) ); /* Call with just -1 terminator. */ printf( "Average is: %d\n", average( -1 ) ); } /* Returns the average of a variable list of integers. */ #ifdef ANSI /* ANSI compatible version */ int average( int first, ... ) { int count = 0, sum = 0, i = first; va_list marker; va_start( marker, first ); /* Initialize variable arguments. */ while( i != -1 ) { sum += i; count++; i = va_arg( marker, int); } va_end( marker ); /* Reset variable arguments. */ return( sum ? (sum / count) : 0 ); } #else /* UNIX compatible version must use old-style definition. */ int average( va_alist ) va_dcl { int i, count, sum; va_list marker; va_start( marker ); /* Initialize variable arguments. */ for( sum = count = 0; (i = va_arg( marker, int)) != -1; count++ ) sum += i; va_end( marker ); /* Reset variable arguments. */ return( sum ? (sum / count) : 0 ); } #endif Output Average is: 3 Average is: 8 Average is: 0 Argument Access Routines See Also vfprintf

[wujingyi2011]

#include <stdio.h> #include <stdarg.h>//va_start、va_end void TestFun(char* pszFormat, ...) { int str_tmp; int args; va_list args; va_start(args, pszFormat); printf("%d\n", va_arg(args, int)); printf("%d\n", va_arg(args, int)); printf("%d\n", va_arg(args, int)); va_end(args); } void main() { TestFun("%d,%d,%d",1,2,3); } 为什么报错？