strtof, strtod, strtold
| Defined in header  <stdlib.h> | ||
| float       strtof( const char *restrict str, char **restrict str_end ); | (since C99) | |
| double      strtod( const char          *str, char          **str_end ); | (until C99) | |
| double      strtod( const char *restrict str, char **restrict str_end ); | (since C99) | |
| long double strtold( const char *restrict str, char **restrict str_end ); | (since C99) | |
Interprets a floating point value in a byte string pointed to by str.
Function discards any whitespace characters (as determined by std::isspace()) 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 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 C locale) (defines significand)
-  (optional) eorEfollowed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent)
 
- binary floating point expression. It consists of the following parts:
- (optional) plus or minus sign
-  0xor0X
- nonempty sequence of hexadecimal digits optionally containing a decimal point character (as determined by the current C locale) (defines significand)
-  (optional) porPfollowed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent)
 
- infinity expression. It consists of the following parts:
- (optional) plus or minus sign
-  INForINFINITYignoring case
 
- not-a-number expression. It consists of the following parts:
- (optional) plus or minus sign
-  NANorNAN(char_sequence)ignoring case of theNANpart. char_sequence can only contain alphanumeric characters. The result is a quiet NaN floating point value.
 
- any other expression that may be accepted by the currently installed C locale
The functions sets the pointer pointed to by str_end to point to the character past the last character interpreted. If str_end is NULL, 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 of str on success. If the converted value falls out of range of corresponding return type, range error occurs and HUGE_VAL, HUGE_VALF or HUGE_VALL is returned. If no conversion can be performed, 0 is returned.
[edit] Example
#include <stdio.h> #include <stdlib.h> int main(void) { char *str = " 111.11 22.22 0X1.BC70A3D70A3D7P+6 1.18973e+4932"; char *str_end; printf("%f\n", strtod(str,&str_end)); printf("str_end --> [%c]\n", *str_end); printf("%f\n", strtod(str_end,&str_end)); printf("%g\n", strtod(str_end,&str_end)); printf("%f\n", strtod(str_end, NULL)); return 0; }
Output:
111.110001 str_end --> [ ] 22.219999 111.11 inf
[edit] See also
| converts a byte string to a floating point value (function) | |
| C++ documentation for strtof, strtod, strtold | |


