Convert a string into a double-precision number
#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 );
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The strtod(), strtof(), and strtold() functions convert the string pointed to by ptr into a double-precision representation:
This function: | Returns: |
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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:
POSIX says that these functions can optionally parse an “n-char sequence” after the NAN. The QNX Neutrino 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.
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, then zero is returned, and errno is set to ERANGE.
These functions return zero and set errno if the input string can't be converted; they don't change errno if no errors occurred. If you want to check for errors, set errno to 0, call the function, and then check errno again. |
#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; }
Safety: | |
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Cancellation point | No |
Interrupt handler | No |
Signal handler | Yes |
Thread | Yes |