##### cppreference.com

##### Search

Create account

##### Namespaces

- Page
- Discussion

##### Variants

##### Views

- View
- Edit
- History

##### Actions

# strtof, strtod, strtold

From cppreference.com
< c‎ | string‎ | byte

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) `e` or `E` followed 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
  - `0x` or `0X`
  - nonempty sequence of hexadecimal digits optionally containing a decimal point character (as determined by the current C locale) (defines significand)
  - (optional) `p` or `P` followed 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
  - `INF` or `INFINITY` ignoring case

- not-a-number expression. It consists of the following parts:

  - (optional) plus or minus sign
  - `NAN` or `NAN(`char_sequence`)` ignoring case of the `NAN` part. 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.

### [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

Run this code

    #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

atof | converts a byte string to a floating point value (function) [edit]
C++ documentation for strtof, strtod, strtold

Retrieved from "http://en.cppreference.com/mwiki/index.php?title=c/string/byte/strtof&oldid=70085"