Manpage of STRTOD

STRTOD

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

NAME

strtod, strtof, strtold - convert ASCII string to floating-point number  

SYNOPSIS

#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():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
 

DESCRIPTION

The strtod(), strtof(), and strtold() functions convert the initial portion of the string pointed to by nptrto double, float, and long doublerepresentation, 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 numberconsists 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 numberconsists 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 infinityis either "INF" or "INFINITY", disregarding case.

A NANis "NAN" (disregarding case) optionally followed by a string, (n-char-sequence), where n-char-sequencespecifies in an implementation-dependent way the type of NAN (see NOTES).  

RETURN VALUE

These functions return the converted value, if any.

If endptris 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 (unless endptris null) the value of nptris 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 ERANGEis stored in errno. If the correct value would cause underflow, zero is returned and ERANGEis stored in errno.  

ERRORS

ERANGE
Overflow or underflow occurred.
 

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
strtod(), strtof(), strtold() Thread safetyMT-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 errnoto 0 before the call, and then determine if an error occurred by checking whether errnohas a nonzero value after the call.

In the glibc implementation, the n-char-sequencethat 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.  

EXAMPLE

See the example on the strtol(3) manual page; the use of the functions described in this manual page is similar.  

SEE ALSO

atof(3), atoi(3), atol(3), nan(3), nanf(3), nanl(3), strtol(3), strtoul(3)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
NOTES
EXAMPLE
SEE ALSO

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Time: 22:27:55 GMT, June 20, 2016