The Open Group Base Specifications Issue 8
IEEE Std 1003.1-2024
Copyright © 2001-2024 The IEEE and The Open Group

NAME

atof — convert a string to a double-precision number

SYNOPSIS

#include <stdlib.h>

double atof(const char *
str);

DESCRIPTION

[CX] [Option Start] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2024 defers to the ISO C standard. [Option End]

The call atof(str) shall be equivalent to:

strtod(str,(char **)NULL),

except that the handling of errors may differ. If the value cannot be represented, the behavior is undefined.

RETURN VALUE

The atof() function shall return the converted value if the value can be represented.

ERRORS

No errors are defined.


The following sections are informative.

EXAMPLES

None.

APPLICATION USAGE

The atof() function is subsumed by strtod() but is retained because it is used extensively in existing code. If the number is not known to be in range, strtod() should be used because atof() is not required to perform any error checking.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

strtod

XBD <stdlib.h>

CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

End of informative text.

 

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