strtof (3)
Leading comments
Copyright (c) 1990, 1991 The Regents of the University of California. All rights reserved. This code is derived from software contributed to Berkeley by the American National Standards Committee X3, on Information Processing Systems. %%%LICENSE_START(BSD_4_CLAUSE_UCB) Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright not...
NAME
strtod, strtof, strtold - convert ASCII string to floating-point numberSYNOPSIS
#include <stdlib.h>
double strtod(const char *nptr, char **endptr);
float strtof(const char *nptr, char **endptr);
long double strtold(const char *nptr, char **endptr);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
strtof(), strtold():
-
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
DESCRIPTION
The strtod(), strtof(), and strtold() functions convert the initial portion of the string pointed to by nptr to double, float, and long double representation, respectively.The expected form of the (initial portion of the) string is optional leading white space as recognized by isspace(3), an optional plus (aq+aq) or minus sign (aq-aq) and then either (i) a decimal number, or (ii) a hexadecimal number, or (iii) an infinity, or (iv) a NAN (not-a-number).
A decimal number consists of a nonempty sequence of decimal digits possibly containing a radix character (decimal point, locale-dependent, usually aq.aq), optionally followed by a decimal exponent. A decimal exponent consists of an aqEaq or aqeaq, followed by an optional plus or minus sign, followed by a nonempty sequence of decimal digits, and indicates multiplication by a power of 10.
A hexadecimal number consists of a "0x" or "0X" followed by a nonempty sequence of hexadecimal digits possibly containing a radix character, optionally followed by a binary exponent. A binary exponent consists of a aqPaq or aqpaq, followed by an optional plus or minus sign, followed by a nonempty sequence of decimal digits, and indicates multiplication by a power of 2. At least one of radix character and binary exponent must be present.
An infinity is either "INF" or "INFINITY", disregarding case.
A NAN is "NAN" (disregarding case) optionally followed by a string, (n-char-sequence), where n-char-sequence specifies in an implementation-dependent way the type of NAN (see NOTES).
RETURN VALUE
These functions return the converted value, if any.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, HUGE_VALL) is returned (according to the 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.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| strtod(), strtof(), strtold() | Thread safety | MT-Safe locale |
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C99.strtod() was also described in C89.
NOTES
Since 0 can legitimately be returned on both success and failure, the calling program should set errno to 0 before the call, and then determine if an error occurred by checking whether errno has a nonzero value after the call.In the glibc implementation, the n-char-sequence that optionally follows "NAN" is interpreted as an integer number (with an optional '0' or '0x' prefix to select base 8 or 16) that is to be placed in the mantissa component of the returned value.