C庫函數 int vfprintf(FILE *stream, const char *format, va_list arg)  發送格式化輸出到一個流使用傳遞給它的參數列表。

聲明

以下是vfprintf()函數的聲明。

int vfprintf(FILE *stream, const char *format, va_list arg)

參數

• stream -- 這是一個文件對象的標識流的指針。

• format -- 這是C字符串，其中包含的文字寫入流，它可以包含嵌入的格式在隨後的附加參數指定的值所取代的標簽和格式化的要求。格式標簽原型： %[flags][width][.precision][length]specifier, 詳細說明如下：

specifier	輸出
c	Character.
d or i	Signed decimal integer
e	Scientific notation (mantissa/exponent) using e character
E	Scientific notation (mantissa/exponent) using E character
f	Decimal floating yiibai
g	Use the shorter of %e or %f.
G	Use the shorter of %E or %f
o	Signed octal
s	String of characters
u	Unsigned decimal integer
x	Unsigned hexadecimal integer
X	Unsigned hexadecimal integer (capital letters)
p	Yiibaier address
n	Nothing printed.
%	Character.

flags	描述
-	Left-justify within the given field width; Right justification is the default (see width sub-specifier).
+	Forces to preceed the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a - sign..
(space)	If no sign is going to be written, a blank space is inserted before the value.
#	Used with o, x or X specifiers the value is preceeded with 0, 0x or 0X respectively for values different than zero. Used with e, E and f, it forces the written output to contain a decimal yiibai even if no digits would follow. By default, if no digits follow, no decimal yiibai is written. Used with g or G the result is the same as with e or E but trailing zeros are not removed.
0	Left-pads the number with zeroes (0) instead of spaces, where padding is specified (see width sub-specifier).

width	描述
(number)	Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger.
*	The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.

.precision	描述
.number	For integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0. For e, E and f specifiers: this is the number of digits to be printed after de decimal yiibai. For g and G specifiers: This is the maximum number of significant digits to be printed. For s: this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered. For c type: it has no effect. When no precision is specified, the default is 1. If the period is specified without an explicit value for precision, 0 is assumed.
.*	The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.

length	描述
h	The argument is interpreted as a short int or unsigned short int (only applies to integer specifiers: i, d, o, u, x and X).
l	The argument is interpreted as a long int or unsigned long int for integer specifiers (i, d, o, u, x and X), and as a wide character or wide character string for specifiers c and s.
L	The argument is interpreted as a long double (only applies to floating yiibai specifiers: e, E, f, g and G).

• arg -- 可變參數列表中的對象。這應該va_start宏定義初始化在<stdarg>。

返回值

如果成功，返回寫入的字符的總數，否則則返回一個負數。

例子

下麵的例子演示了如何使用 vfprintf() 函數。

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

void WriteFrmtd(FILE *stream, char *format, ...)
{
   va_list args;

   va_start(args, format);
   vfprintf(stream, format, args);
   va_end(args);
}

int main ()
{
   FILE *fp;

   fp = fopen("file.txt","w");

   WriteFrmtd(fp, "This is just one argument %d 
", 10);

   fclose(fp);
   
   return(0);
}

讓我們編譯和運行上麵的程序，這將打開一個文件 file.txt 寫在當前目錄，並且將其寫入以下內容：

This is just one argument 10