strtod(), strtof(), strtold()
Convert a string into a double-precision number
Synopsis:
#include <stdlib.h>
double strtod( const char *ptr,
char **endptr );
float strtof( const char *ptr,
char **endptr );
long double strtold( const char *ptr,
char **endptr );
Arguments:
- ptr
- A pointer to the string to parse.
- endptr
- If this argument isn't NULL, the function stores in it a pointer to the first unrecognized character found in the string.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The strtod(), strtof(), and strtold() functions convert the string pointed to by ptr into a double-precision representation:
| This function: | Returns: |
|---|---|
| strtod() | double |
| strtof() | float |
| strtold() | long double |
These functions skip any leading white space, and then look for a subject sequence that consists of an optional plus or minus sign followed by one of the following:
- a non-empty sequence of decimal digits optionally containing a radix character, then an optional exponent part
- 0x or 0X, then a non-empty sequence of hexadecimal digits optionally containing a radix character, then an optional binary exponent part
- INF or INFINITY, ignoring case
- NAN, ignoring case
Note:POSIX says that these functions can optionally parse an
n-char sequence
after the NAN. The QNX OS versions don't interpret an n-char sequence, and the result is equivalent to specifying NAN without the n-char sequence.
The conversion ends at the first unrecognized character. If endptr isn't NULL, a pointer to the unrecognized character is stored in the object endptr points to.
Returns:
The converted value. If the correct value would cause overflow, plus or minus HUGE_VAL is returned according to the sign, and errno is set to ERANGE. If the correct value would cause underflow, a value with a magnitude no greater than the smallest normalized positive number in the return type is returned and errno is set to ERANGE.
Errors:
- ERANGE
- The value to be returned would cause overflow or underflow.
- EINVAL
- No conversion could be performed.
Examples:
#include <stdio.h>
#include <stdlib.h>
int main( void )
{
double pi;
pi = strtod( "3.141592653589793", NULL );
printf( "pi=%17.15f\n",pi );
return EXIT_SUCCESS;
}
Classification:
| Safety: | |
|---|---|
| Cancellation point | No |
| Signal handler | Yes |
| Thread | Yes |