fprintf() - C语言库函数

C库函数 int fprintf(FILE *stream, const char *format, ...) 发送格式化输出到一个流。

声明

以下是声明 fprintf() 函数的功能。

int fprintf(FILE *stream, const char *format, ...)

参数

  • stream -- 这是一个文件对象的标识流的指针。

  • format - 这是C字符串,其中包含的文字写入流。它可以包含嵌入的格式在随后的附加参数指定的值所取代的标签和格式化所要求。格式标签的原型是 %[flags][width][.precision][length]specifier, 如下列表所示:

指示符 输出
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.
标识 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).
  • additional arguments -- 根据格式字符串,函数可能会想到一系列的额外的参数,每个包含一个值,而不是插入的格式参数中指定的标记每个%,如果有的话。应该有相同数量的%预期值的标签的数量的这些参数。

返回值

如果成功,返回写入的字符的总数,否则则返回一个负数。

例子

下面的例子显示fprintf() 函数功能的用法。

#include <stdio.h>#include <stdlib.h>int main(){ FILE * fp; fp = fopen ("file.txt", "w+"); fprintf(fp, "%s %s %s %d", "We", "are", "in", 2012); fclose(fp); return(0);}

让我们编译和运行上面的程序,这将创建一个文件 file.txt 中包含以下内容:

We are in 2012