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<cstdlib>
double atof ( const char * str );
Convert string to double
Parses the C string str interpreting its content as a floating point number and returns its value as a double.
The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes as many characters as possible that are valid following a syntax resembling that of floating point literals, and interprets them as a numerical value. The rest of the string after the last valid character is ignored and has no effect on the behavior of this function.
A valid floating point number for atof is formed by a succession of:
- An optional plus or minus sign
- A sequence of digits, optionally containing a decimal-point character
- An optional exponent part, which itself consists on an 'e' or 'E' character followed by an optional sign and a sequence of digits.
If the first sequence of non-whitespace characters in str does not form a valid floating-point number as just defined, or if no such sequence exists because either str is empty or contains only whitespace characters, no conversion is performed.
Parameters
- str
- C string beginning with the representation of a floating-point number.
Return Value
On success, the function returns the converted floating point number as a double value.
If no valid conversion could be performed, or if the correct value would cause underflow, a zero value (0.0) is returned.
If the correct value is out of the range of representable values, a positive or negative HUGE_VAL is returned.
Example
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/* atof example: sine calculator */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main ()
{
double n,m;
double pi=3.1415926535;
char szInput [256];
printf ( "Enter degrees: " );
gets ( szInput );
n = atof ( szInput );
m = sin (n*pi/180);
printf ( "The sine of %f degrees is %f\n" , n, m );
return 0;
}
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Output:
Enter degrees: 45
The sine of 45.000000 degrees is 0.707101
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See also
| strtod | Convert string to double (function) |
| atoi | Convert string to integer (function) |
| atol | Convert string to long integer (function) |
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