STRTOD(3) | Library Functions Manual | STRTOD(3)

# NAME

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

# 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);

# 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 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.

Alternatively, if the portion of the string following the optional plus or minus sign begins with “INF” or “NAN”, ignoring case, it is interpreted as an infinity or a quiet NaN, respectively. The syntax “NAN(s)”, where s is an alphanumeric string, produces the same value as the call `nan`("s"); (respectively, `nanf`("s"); and `nanl`("s");).

In any of the above cases, leading whitespace 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.

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` 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.

# SEE ALSO

atof(3), atoi(3), atol(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”).

# CAVEATS

On systems other than OpenBSD, the `LC_NUMERIC` locale(1) category can cause parsing failures; see CAVEATS in setlocale(3) for details.

September 11, 2022 | Debian