atol(), atoll() and atof() functions in C/C++

atol(): This function converts a C-type string, passed as an argument to function call, to a long integer. It parses the C-string str interpreting its content as an integral number, which is returned as a value of type long int. The function discards the whitespace characters present at the beginning of the string until a non-whitespace character is found. If the sequence of non-whitespace characters in C-string str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed and zero is returned.

Syntax:

long int atol ( const char * str )

Parameters: The function accepts one mandatory parameter str which is the representation of an integral number.

Return Value: The function returns the converted integral number as a long int. If no valid conversion can be performed, it returns zero.

// CPP program to illustrate 
// working of atol() function. 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // char array of numbers 
    char str1[] = "5672345"; 
  
    // Function calling to convert to a long int 
    long int num1 = atol(str1); 
  
    cout << "Number is " << num1 << "\n"; 
  
    // char array of numbers of spaces 
    char str2[] = "10000002  0"; 
  
    // Function calling to convert to a long int 
    long int num2 = atol(str2); 
  
    cout << "Number is " << num2 << "\n"; 
    return 0; 
} 

Output:

Number is 5672345
Number is 10000002

atoll(): This function converts a C-type string, passed as an argument to function call, to a long long integer. It parses the C-string str interpreting its content as an integral number, which is returned as a value of type long long int. The function discards the whitespace characters present at the beginning of the string until a non-whitespace character is found.
If the sequence of non-whitespace characters in C-string str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed and zero is returned.

Syntax:

long long int atoll ( const char * str )

Parameters: The function accepts a mandatory parameter str which is the representation of an integral number.

Return Value: The function returns the converted integral number as a long long int. If no valid conversion can be performed, it returns zero.

// CPP program to illustrate 
// working of atol() function. 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // char array of numbers 
    char big_num1[] = "8239206483232728"; 
  
    // Function calling to convert to a long int 
    long long int num1 = atoll(big_num1); 
  
    cout << "Number is " << num1 << "\n"; 
  
    // char array of numbers of spaces 
    char big_num2[] = "100000 9 1324100"; 
  
    // Function calling to convert to a long int 
    long long int num2 = atoll(big_num2); 
  
    cout << "Number is " << num2 << "\n"; 
    return 0; 
} 

Output:

Number is 8239206483232728
Number is 100000

atof() function: This function converts a C-type string, passed as an argument to function call, to double. It parses the C-string str interpreting its content as a floating point number, which is returned as a value of type double. The function discards the whitespace characters present at the beginning of the string until a non-whitespace character is found. If the sequence of non-whitespace characters in C-string str is not a valid floating point number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed and 0.0 is returned.

Syntax:

double atof ( const char * str )

Parameters: The function accepts a single mandatory parameter str which is the representation of a floating point number.

Return Value:The function returns the converted floating point number as a double value. If no valid conversion can be performed, the function returns zero (0.0).

Return Value:

// CPP program to illustrate 
// working of atol() function. 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // char array 
    char pi[] = "3.1415926535"; 
  
    // Calling function to convert to a double 
    double pi_val = atof(pi); 
  
    // prints the double value 
    cout << "Value of pi = " << pi_val << "\n"; 
  
    // char array 
    char acc_g[] = "9.8"; 
  
    // Calling function to convert to a double 
    double acc_g_val = atof(acc_g); 
  
    // prints the double value 
    cout << "Value of acceleration due to gravity = "
         << acc_g_val << "\n"; 
    return 0; 
} 

Output:

Value of pi = 3.14159
Value of acceleration due to gravity = 9.8

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