NAME

strtod, strtof, strtold — convert ASCII string to double, float, or long double

LIBRARY

Standard C Library (libc, -lc)

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);

DESCRIPTION

The strtod() function converts the initial portion of the string pointed to by nptr to double representation.

The strtof() function converts the initial portion of the string pointed to by nptr to float representation.

The strtold() function converts the initial portion of the string pointed to by nptr to long double representation.

The expected form of the string is an optional plus (‘+’) or minus sign (‘-’) followed by one of the following:

• a sequence of digits optionally containing a decimal-point character, optionally followed by an exponent. An exponent consists of an ‘E’ or ‘e’, followed by an optional plus or minus sign, followed by a sequence of digits.
• one of INF or INFINITY, ignoring case.
• one of NAN or NAN(n-char-sequence-opt), ignoring case. This implementation currently does not interpret such a sequence.

Leading white-space characters in the string (as defined by the isspace(3) function) are skipped.

RETURN VALUES

The strtod(), strtof(), and strtold() functions return the converted value, if any.

A character sequence INF or INFINITY is converted to infinity, if supported, else to the largest finite floating-point number representable on the machine (i.e., VAX).

A character sequence NAN or NAN(n-char-sequence-opt) is converted to a quiet NaN, if supported, else remains unrecognized (i.e., VAX).

If endptr is not NULL, a pointer to the character after the last character used in the conversion is stored in the location referenced by endptr.

If no conversion is performed, zero is returned and the value of nptr is stored in the location referenced by endptr.

If the correct value would cause overflow, plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the return type and sign of the value), and ERANGE is stored in errno. If the correct value would cause underflow, zero is returned and ERANGE is stored in errno.

ERRORS

[ERANGE]

Overflow or underflow occurred.

SEE ALSO

atof(3), atoi(3), atol(3), math(3), strtol(3), strtoul(3)

STANDARDS

The strtod() function conforms to ANSI X3.159-1989 (“ANSI C89”). The strtof() and strtold() functions conform to ISO/IEC 9899:1999 (“ISO C99”).

HISTORY

The strtof() and strtold() functions appeared in NetBSD 4.0.