atof 函数参考

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

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

/* 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; }

Output:

Enter degrees: 45 The sine of 45.000000 degrees is 0.707101