Namespaces
Variants

strfromf, strfromd, strfroml

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< c ‎ | string ‎ | byte
C
Strings library
Null-terminated byte strings
Functions
Character manipulation
Conversions to and from numeric formats
(C99) (C99)
(C99) (C99)
strfromf strfromd strfroml
(C23) (C23) (C23)
String manipulation
String examination
Memory manipulation
Miscellaneous
(C11) (C11)
定义于头文件 <stdlib.h>
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)

将浮点数值转换为字节字符串。

这些函数等效于 snprintf ( s, n, format, fp ) ，不同之处在于格式字符串只能包含字符 % 、不包含星号 * 的可选精度说明符，以及适用于 double 、 float 或 long double 类型的转换说明符（ a 、 A 、 e 、 E 、 f 、 F 、 g 、 G 之一），具体类型由函数后缀指明（而非通过长度修饰符）。使用这些函数时若采用其他格式字符串将导致未定义行为。

目录

参数

s - 指向要写入的字符串的指针
n - 最多可写入 n - 1 个字符，外加空终止符
format - 指向空终止字节字符串的指针，指定如何解释数据
fp - 要转换的浮点数值

返回值

当 n 足够大时本应写入的字符数（不计算终止空字符）。因此，当且仅当返回值非负且小于 n 时，说明空终止输出已完全写入。

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"

参考

  • C23 标准 (ISO/IEC 9899:2024):
  • 7.24.1.3 strfromd、strfromf 和 strfroml 函数

参见

(C99) (C11) (C11) (C11) (C11)
将格式化输出打印到 标准输出 、文件流或缓冲区
(函数)
(C99) (C99)
将字节字符串转换为浮点数值
(函数)