strfromf, strfromd, strfroml

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< c | string | byte
 
C
 
字符串库
 
空终止字节字符串
 
<tbody> </tbody>
在标头 <stdlib.h> 定义
int strfromf( char* restrict s, size_t n, const char* restrict format, float fp );
 (C23 起)
int strfromd( char* restrict s, size_t n, const char* restrict format, double fp );
 (C23 起)
int strfroml( char* restrict s, size_t n, const char* restrict format, long double fp );
 (C23 起)
See More

将浮点数转换为字节字符串。

这些函数等价于 snprintf(s, n, format, fp)，但格式字符串应当仅包含字符 %，可选的不包含星号 * 的精度，和以下转换指示符之一：a、A、e、E、f、F、g 和 G，分别使其适用于函数后缀（而非长度修饰符）所指定的类型（double、float 或 long double）。以其他任何格式字符串调用这些函数将导致未定义行为。

参数

s - 指向将写入的字符串
n - 最多写入 n - 1 个字符和空终结符
format - 指向空终结字节字符串的指针，指定如何判读数据
fp - 欲转换的浮点数

返回值

假设 n 足够大时将会写入的字符数量，不计入终结的空字符。因而，当且仅当返回值非负且小于 n 时，才会完整写入带空终结的输出。

示例

运行此代码
#include <stdio.h>
#include <stdlib.h>

int main()
{
    char buffer[32];
    int written;
    const char* format[] = {"%a", "%A", "%e", "%E", "%f", "%F", "%g", "%G"};

    for (size_t fmt = 0; fmt != sizeof format / sizeof format[0]; ++fmt)
    {
        written = strfromf(buffer, sizeof buffer, format[fmt], 3.1415f);
        printf("strfromf(... %s ...) = %2i, buffer: \"%s\"\n",
               format[fmt], written, buffer);
    }
    puts("");

    for (size_t fmt = 0; fmt != sizeof format / sizeof format[0]; ++fmt)
    {
        written = strfromd(buffer, sizeof buffer, format[fmt], 3.1415);
        printf("strfromd(... %s ...) = %2i, buffer: \"%s\"\n",
               format[fmt], written, buffer);
    }
    puts("");

    for (size_t fmt = 0; fmt != sizeof format / sizeof format[0]; ++fmt)
    {
        written = strfroml(buffer, sizeof buffer, format[fmt], 3.1415);
        printf("strfroml(... %s ...) = %2i, buffer: \"%s\"\n",
               format[fmt], written, buffer);
    }
}

输出： 

strfromf(... %a ...) = 13, buffer: "0x1.921cacp+1"
strfromf(... %A ...) = 13, buffer: "0X1.921CACP+1"
strfromf(... %e ...) = 12, buffer: "3.141500e+00"
strfromf(... %E ...) = 12, buffer: "3.141500E+00"
strfromf(... %f ...) =  8, buffer: "3.141500"
strfromf(... %F ...) =  8, buffer: "3.141500"
strfromf(... %g ...) =  6, buffer: "3.1415"
strfromf(... %G ...) =  6, buffer: "3.1415"

strfromd(... %a ...) = 20, buffer: "0x1.921cac083126fp+1"
strfromd(... %A ...) = 20, buffer: "0X1.921CAC083126FP+1"
strfromd(... %e ...) = 12, buffer: "3.141500e+00"
strfromd(... %E ...) = 12, buffer: "3.141500E+00"
strfromd(... %f ...) =  8, buffer: "3.141500"
strfromd(... %F ...) =  8, buffer: "3.141500"
strfromd(... %g ...) =  6, buffer: "3.1415"
strfromd(... %G ...) =  6, buffer: "3.1415"

strfroml(... %a ...) = 20, buffer: "0xc.90e5604189378p-2"
strfroml(... %A ...) = 20, buffer: "0XC.90E5604189378P-2"
strfroml(... %e ...) = 12, buffer: "3.141500e+00"
strfroml(... %E ...) = 12, buffer: "3.141500E+00"
strfroml(... %f ...) =  8, buffer: "3.141500"
strfroml(... %F ...) =  8, buffer: "3.141500"
strfroml(... %g ...) =  6, buffer: "3.1415"
strfroml(... %G ...) =  6, buffer: "3.1415"

引用

  • C23 标准（ISO/IEC 9899:2024）：
  • 7.24.1.3 The strfromd, strfromf, and strfroml functions

参阅

(C99)(C11)(C11)(C11)(C11)
 打印格式化输出到 stdout、文件流或缓冲区
(函数) [编辑]
(C99)(C99)
 将字节字符串转换成浮点数
(函数) [编辑]