strtod#

Synopsis#

#include <stdlib.h>

double strtod(const char *restrict nptr, char **restrict endptr);

float strtof(const char *restrict nptr, char **restrict endptr);

long double strtold(const char *restrict nptr, char **restrict endptr);

Status#

Partially implemented

Conformance#

IEEE Std 1003.1-2017

Description#

These functions shall convert the initial portion of the string pointed to by nptr to double, float, and long double representation, respectively. First, they decompose the input string into three parts:

An initial, possibly empty, sequence of white-space characters (as specified by isspace())
A subject sequence interpreted as a floating-point constant or representing infinity or NaN
A final string of one or more unrecognized characters, including the terminating NULL character of the input string

Then they shall attempt to convert the subject sequence to a floating-point number, and return the result.

The expected form of the subject sequence is an optional + or - sign, then one of the following:

A non-empty sequence of decimal digits optionally containing a radix character; then an optional exponent part consisting of the character e or the character E, optionally followed by a + or - character, and then followed by one or more decimal digits
A 0x or 0X, then a non-empty sequence of hexadecimal digits optionally containing a radix character; then an optional binary exponent part consisting of the character p or the character P, optionally followed by a + or - character, and then followed by one or more decimal digits
One of INF or INFINITY, ignoring case
One of NaN or NaN(n-char-sequenceopt), ignoring case in the NaN part, where:

    n-char-sequence:
        digit
        nondigit
        n-char-sequence digit
        n-char-sequence nondigit

The subject sequence is defined as the longest initial subsequence of the input string, starting with the first non-white-space character, that is of the expected form. The subject sequence contains no characters if the input string is not of the expected form.

If the subject sequence has the expected form for a floating-point number, the sequence of characters starting with the first digit or the decimal-point character (whichever occurs first) shall be interpreted as a floating constant of the C language, except that the radix character shall be used in place of a period, and that if neither an exponent part nor a radix character appears in a decimal floating-point number, or if a binary exponent part does not appear in a hexadecimal floating-point number, an exponent part of the appropriate type with value zero is assumed to follow the last digit in the string. If the subject sequence begins with a <hyphen-minus>, the sequence shall be interpreted as negated. A character sequence INF or INFINITY shall be interpreted as an infinity, if representable in the return type, else as if it were a floating constant that is too large for the range of the return type. A character sequence NaN or NaN(n-char-sequenceopt) shall be interpreted as a quiet NaN, if supported in the return type, else as if it were a subject sequence part that does not have the expected form; the meaning of the n-char sequences is implementation-defined. A pointer to the final string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.

If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the value resulting from the conversion is correctly rounded.

The radix character is defined in the current locale (category LC_NUMERIC). In the POSIX locale, or in a locale where the radix character is not defined, the radix character shall default to a <period> (.).

In other than the C or POSIX locale, additional locale-specific subject sequence forms may be accepted.

If the subject sequence is empty or does not have the expected form, no conversion shall be performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.

These functions shall not change the setting of errno if successful. Since 0 is returned on error and is also a valid return on success, an application wishing to check for error situations should set errno to 0, then call strtod(), strtof(), or strtold(), then check errno.

Return value#

Upon successful completion, these functions shall return the converted value. If no conversion could be performed, 0 shall be returned, and errno may be set to EINVAL.

If the correct value is outside the range of representable values, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL shall be returned (according to the sign of the value), and errno shall be set to ERANGE.

If the correct value would cause an underflow, a value whose magnitude is no greater than the smallest normalized positive number in the return type shall be returned and errno set to ERANGE.

Errors#

These functions shall fail if:

ERANGE - The value to be returned would cause overflow or underflow.

These functions may fail if:

EINVAL - No conversion could be performed.

Tests#

Untested

Known bugs#

None