Syntax
#include <stdlib.h> double strtod(const char *nptr, char **endptr);Description
strtod converts a character string to a double-precision value. The parameter nptr points to a sequence of characters that can be interpreted as a numerical value of the type double. This function stops reading the string at the first character that it cannot recognize as part of a number. This character can be the null character at the end of the string.
The strtod function expects nptr to point to a string with the following form:
┌──────────────────────────────────────────────────────────────────────────────┐
│ │
│ >>──┬─────────────┬──┬───┬──┬───────────────────────────┬──>
│
│ └─white-space─┘ ├─+─┤ ├─digits──┬───┬──┬────────┬─┤ │
│ └─┴─┘ │ └─.─┘ └─digits─┘ │ │
│ └─.──digits─────────────────┘ │
│ │
│ >──┬──────────────────────┬──>< │
│ └─┬─e─┬──┬───┬──digits─┘ │
│ └─E─┘ ├─+─┤ │
│ └─┴─┘ │
│ │
└──────────────────────────────────────────────────────────────────────────────┘
The first character that does not fit this form stops the scan. The radix character is defined in the program's locale by the category LC_NUMERIC.
strtod returns the value of the floating-point number, except when the representation causes an underflow or overflow. For an overflow, it returns -HUGE_VAL or +HUGE_VAL; for an underflow, it returns 0.
In both cases, errno is set to ERANGE, depending on the base of the value. If the string pointed to by nptr does not have the expected form, no conversion is performed and the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a NULL pointer.
strtod does not fail if a character other than a digit follows an E or e read in as an exponent. For example, 100elf will be converted to the floating-point value 100.0.
This example converts the strings to a double value. It prints out the converted value and the substring that stopped the conversion.
#include <stdlib.h>
#include <stdio.h>
int main(void)
{
char *string,*stopstring;
double x;
string = "3.1415926This stopped it";
x = strtod(string, &stopstring);
printf("string = %s\n", string);
printf(" strtod = %f\n", x);
printf(" Stopped scan at %s\n\n", stopstring);
string = "100ergs";
x = strtod(string, &stopstring);
printf("string = \"%s\"\n", string);
printf(" strtod = %f\n", x);
printf(" Stopped scan at \"%s\"\n\n", stopstring);
return 0;
/****************************************************************************
The output should be:
string = 3.1415926This stopped it
strtod = 3.141593
Stopped scan at This stopped it
string = "100ergs"
strtod = 100.000000
Stopped scan at "ergs"
****************************************************************************/
}
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