The strtod() is a builtin function in C and C++ STL which interprets the contents of the string as a floating point number and return its value as a double.
It sets a pointer to point to the first character after the last valid character of the string, only if there is any, otherwise it sets the pointer to null.
Syntax:
double strtod(str, &end)
Parameters:
str: It specifies the string which has the representation of a floating point number.
end: It is specified the parameter that refers to an already allocated object of type char*.
Return Value: It returns a double value, which is converted from a string, and 0, if no valid conversion can be performed.
Below programs illustrate the above function:
Program 1:
// C++ program to illustrate the // strtod() function #include <cstdlib> #include <iostream> using namespace std;
int main()
{ char str[] = "11.03e 0mn" ;
char * end;
double number;
number = strtod (str, &end);
cout << "number = " << str << endl;
cout << "double = " << number << endl;
cout << "end string = " << end << endl;
return 0;
} |
number = 11.03e 0mn double = 11.03 end string = e 0mn
Program 2:
// C++ program to illustrate the // strtod() function without trailing characters #include <cstdlib> #include <iostream> using namespace std;
int main()
{ char str[] = "4.06" ;
char * end;
double number;
number = strtod (str, &end);
cout << "number= " << str << endl;
cout << "double= " << number << endl;
// If end is not Null
if (*end) {
cout << end;
}
// If end is Null
else {
cout << "null" ;
}
return 0;
} |
number= 4.06 double= 4.06 null
Program 3:
strtod() function with exponents and hexadecimals
// C++ program to illustrate the // strtod() function with exponents and hexadecimals #include <cstdlib> #include <cstring> #include <iostream> using namespace std;
int main()
{ // initialize a exponential value
char str[] = "-89.04e-3win gfg" ;
char * end;
double number;
number = strtod (str, &end);
cout << "str = " << str << endl;
cout << "double = " << number << endl;
cout << "end string = " << end << endl
<< endl;
// initialize a new hexadecimal value
strcpy (str, "1998gupta.1204ishwar" );
number = strtod (str, &end);
cout << "str = " << str << endl;
cout << "double = " << number << endl;
cout << "end string = " << end << endl;
return 0;
} |
str = -89.04e-3win gfg double = -0.08904 end string = win gfg str = 1998gupta.1204ishwar double = 1998 end string = gupta.1204ishwar
Program 4:
// C++ program to illustrate the // strtod() function for Infinity and NaN #include <cstdlib> #include <iostream> using namespace std;
int main()
{ char * end;
cout << "Infinity"
<< " to double = " << strtod ( "infinity" , &end) << endl;
cout << "end string = " << end << endl
<< endl;
cout << "Infpqrs"
<< " to double = " <<
strtod ( "Infpqrs" , &end) << endl;
cout << "end string = " << end << endl
<< endl;
cout << "NaN11x"
<< " to double = " << strtod ( "NaN11x" , &end) << endl;
cout << "end string = " << end << endl
<< endl;
return 0;
} |
Infinity to double = inf end string = Infpqrs to double = inf end string = pqrs NaN11x to double = nan end string = 11x
Program 5:
strtod() function with leading whitespace
// C++ program to illustrate the // strtod() function with leading whitespace #include <cstdlib> #include <iostream> using namespace std;
int main()
{ char * end;
cout << "99.99"
<< " to double = " << strtod ( " 19.99" , &end) << endl;
// end pointer is set to null
cout << "end string = " << end << endl
<< endl;
// Returns 0 because of invalid conversion
cout << "xyz1.80"
<< " to double = " << strtod ( "xyz1.80" , &end) << endl;
cout << "end string = " << end << endl
<< endl;
return 0;
} |
99.99 to double = 19.99 end string = xyz1.80 to double = 0 end string = xyz1.80