Movatterモバイル変換

[0]ホーム
URL:

cppreference.com
Namespaces
Variants
    Actions

      strtof, strtod, strtold

      From cppreference.com
      <c‎ |string‎ |byte
       
       
       
       
      Defined in header<stdlib.h>
      float       strtof(constchar*restrict str,char**restrict str_end);
      		 (1)(since C99)
      (2)
      double      strtod(constchar*          str,char**          str_end);
      		(until C99)
      double      strtod(constchar*restrict str,char**restrict str_end);
      		(since C99)
      longdouble strtold(constchar*restrict str,char**restrict str_end);
      		 (3)(since C99)

      Interprets a floating-point value in a byte string pointed to bystr.

      Function discards any whitespace characters (as determined byisspace) until first non-whitespace character is found. Then it takes as many characters as possible to form a valid floating-point representation and converts them to a floating-point value. The valid floating-point value can be one of the following:

      • decimal floating-point expression. It consists of the following parts:
      • (optional) plus or minus sign
      • nonempty sequence of decimal digits optionally containing decimal-point character (as determined by the current Clocale) (defines significand)
      • (optional)e orE followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base10)
      • hexadecimal floating-point expression. It consists of the following parts:
      • (optional) plus or minus sign
      • 0x or0X
      • nonempty sequence of hexadecimal digits optionally containing a decimal-point character (as determined by the current Clocale) (defines significand)
      • (optional)p orP followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base2)
      • infinity expression. It consists of the following parts:
      • (optional) plus or minus sign
      • INF orINFINITY ignoring case
      • not-a-number expression. It consists of the following parts:
      • (optional) plus or minus sign
      • NAN orNAN(char_sequence ) ignoring case of theNAN part.char_sequence can only contain digits, Latin letters, and underscores. The result is a quiet NaN floating-point value.
      		(since C99)
      • any other expression that may be accepted by the currently installed Clocale.

      The functions sets the pointer pointed to bystr_end to point to the character past the last character interpreted. Ifstr_end is a null pointer, it is ignored.

      Contents

      [edit]Parameters

      str - pointer to the null-terminated byte string to be interpreted
      str_end - pointer to a pointer to character

      [edit]Return value

      Floating-point value corresponding to the contents ofstr on success. If the converted value falls out of range of corresponding return type, range error occurs (errno is set toERANGE) andHUGE_VAL,HUGE_VALF orHUGE_VALL is returned. If no conversion can be performed,​0​ is returned.

      [edit]Example

      Run this code
      #include <errno.h>#include <stdio.h>#include <stdlib.h> int main(void){// parsing with error handlingconstchar* p="111.11 -2.22 Nan nan(2) inF 0X1.BC70A3D70A3D7P+6  1.18973e+4932zzz";printf("Parsing '%s':\n", p);char* end=NULL;for(double f= strtod(p,&end); p!= end; f= strtod(p,&end)){printf("'%.*s' -> ",(int)(end- p), p);        p= end;if(errno==ERANGE){printf("range error, got ");errno=0;}printf("%f\n", f);} // parsing without error handlingprintf("\"  -0.0000000123junk\"  -->  %g\n", strtod("  -0.0000000123junk",NULL));printf("\"junk\"                 -->  %g\n", strtod("junk",NULL));}

      Possible output:

      Parsing '111.11 -2.22 Nan nan(2) inF 0X1.BC70A3D70A3D7P+6  1.18973e+4932zzz':'111.11' -> 111.110000' -2.22' -> -2.220000' Nan' -> nan' nan(2)' -> nan' inF' -> inf' 0X1.BC70A3D70A3D7P+6' -> 111.110000'  1.18973e+4932' -> range error, got inf"  -0.0000000123junk"  -->  -1.23e-08"junk"                 -->  0

      [edit]References

      • C23 standard (ISO/IEC 9899:2024):
      • 7.22.1.3 The strtod, strtof, and strtold functions (p: TBD)
      • C17 standard (ISO/IEC 9899:2018):
      • 7.22.1.3 The strtod, strtof, and strtold functions (p: 249-251)
      • C11 standard (ISO/IEC 9899:2011):
      • 7.22.1.3 The strtod, strtof, and strtold functions (p: 342-344)
      • C99 standard (ISO/IEC 9899:1999):
      • 7.20.1.3 The strtod, strtof, and strtold functions (p: 308-310)
      • C89/C90 standard (ISO/IEC 9899:1990):
      • 4.10.1.4 The strtod function

      [edit]See also

      converts a byte string to a floating-point value
      (function)[edit]
      (C99)(C95)(C99)
      		 converts a wide string to a floating-point value
      (function)[edit]
      C++ documentation forstrtof,strtod,strtold
      Retrieved from "https://en.cppreference.com/mwiki/index.php?title=c/string/byte/strtof&oldid=178833"
      [8]ページ先頭
      ©2009-2025 Movatter.jp