strfromf, strfromd, strfroml

 

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符號索引

 

字串庫

空終止位元組字串

空終止多位元組字串

空終止寬字串

 

空終止位元組字串

函式
字元操作
isalnum isalpha islower isupper isdigit isxdigit isblank (C99)	iscntrl isgraph isspace isprint ispunct tolower toupper
與數字格式相互轉換
atoiatolatoll (C99) atof strtolstrtoll (C99) strtoulstrtoull (C99)	strtoimaxstrtoumax (C99)(C99) strtofstrtodstrtold (C99)(C99) strfromfstrfromdstrfroml (C23)(C23)(C23)
字串操作
strcpystrcpy_s (C11) strncpystrncpy_s (C11) strcatstrcat_s (C11)	strncatstrncat_s (C11) strxfrm strdup (C23) strndup (C23)
字串檢查
strlenstrnlen_s (C11) strcmp strncmp strcoll strchr strrchr	strspn strcspn strpbrk strstr strtokstrtok_s (C11)
記憶體操作
memchr memcmp memsetmemset_explicitmemset_s (C23)(C11)	memcpymemcpy_s (C11) memmovememmove_s (C11) memccpy (C23)
雜項
strerrorstrerror_sstrerrorlen_s (C11)(C11)

 

在標頭檔案 <stdlib.h> 中定義
int strfromf( char* restrict s, size_t n, const char* restrict format, float fp );		(自 C23 起)
int strfromd( char* restrict s, size_t n, const char* restrict format, double fp );		(自 C23 起)
int strfroml( char* restrict s, size_t n, const char* restrict format, long double fp );		(自 C23 起)

轉換浮點值為位元組字串。

這些函式等價於 snprintf(s, n, format, fp)，但格式字串應只包含字元 %、一個可選的不含星號 * 的精度，以及 a、A、e、E、f、F、g 或 G 之一的轉換指定符，該指定符適用於函式字尾所指示的型別（double、float 或 long double），而非由長度修飾符指示。以任何其他格式字串使用這些函式導致未定義行為。

引數

s	-	要寫入的字元字串指標
n	-	至多可以寫入 n - 1 個字元，外加空終止符
format	-	指向指定如何解釋資料的空終止位元組字串的指標
fp	-	要轉換的浮點值

返回值

若 n 足夠大，本應寫入的字元數，不計終止空字元。因此，當且僅當返回的值為非負且小於 n 時，空終止輸出已被完全寫入。

示例

執行此程式碼

#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);
    }
}

輸出

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 標準 (ISO/IEC 9899:2024)

• 7.24.1.3 The strfromd, strfromf, and strfroml functions

參閱

printffprintfsprintfsnprintfprintf_sfprintf_ssprintf_ssnprintf_s (C99)(C11)(C11)(C11)(C11)	將格式化輸出列印到 stdout、檔案流或緩衝區 (函式)
strtofstrtodstrtold (C99)(C99)	將位元組字串轉換為浮點值 (函式)