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

In C/C++, atol(), atoll(), and atof() are functions used to convert strings to numbers of different types. These functions are Standard Library functions. In this article, we will learn these String-to-number conversion functions in C/C++.

1. atol() in C/C++

The atol() function converts a C-style string (array of characters), passed as an argument to atol() function, to a long integer. It converts the C-string str to a value of type long int by interpreting the characters of the string as numerical values. It discards the leading whitespace characters until a non-whitespace character is found.

Syntax

long int **atol ( const char * _str );

**Parameters

• The function accepts one mandatory parameter **str which represents an integral number.

**Return Value

• The function returns the long int representation of the string.
• It returns '0' if no valid conversion can be performed.

**Note: If the C-string str passed to atol() function is either empty or contains only whitespace characters, it is not a valid integral number, no conversion will be performed and it will return zero.

Example: Program to Illustrate the Working of atol() Function.

C++ `

// 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;

}

C

// C program to illustrate // working of atol() function. #include <stdio.h> // Include this header for atol function #include <stdlib.h>

int main() { // char array of numbers char str1[] = "5672345";

// Function calling to convert to a long int
long int num1 = atol(str1);

printf("Number is %ld\n", num1);

// char array of numbers without spaces
char str2[] = "10000002 0";

// Function calling to convert to a long int
long int num2 = atol(str2);

printf("Number is %ld\n", num2);

return 0;

}

`

Output

Number is 5672345 Number is 10000002

2. atoll() in C/C++

The atoll() function converts a C-style string, passed as an argument to atol() function, to a long long integer. It converts the C-string str to a value of type long long int by interpreting the characters of the string as numerical values. It discards the leading whitespace characters until a non-whitespace character is found.

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 long long int representation of the string.
• It returns '0' if no valid conversion can be performed.

**Note: If the C-string str passed to atol() function is either empty or contains only whitespace characters, it is not a valid integral number, no conversion will be performed and it will return zero.

Example: Program to Illustrate the Working of atoll() Function.

C++ `

// CPP program to illustrate // working of atoll() 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;

}

C

// C program to illustrate // working of atol() function. #include <stdio.h> // Include this header for atoll function #include <stdlib.h>

int main() { // char array of numbers char big_num1[] = "8239206483232728";

// Function calling to convert to a long long int
long long int num1 = atoll(big_num1);

printf("Number is %lld\n", num1);

// char array of numbers without spaces
char big_num2[] = "100000 9 1324100";

// Function calling to convert to a long long int
long long int num2 = atoll(big_num2);

printf("Number is %lld\n", num2);

return 0;

}

`

Output

Number is 8239206483232728 Number is 100000

3. atof() in C/C++

The atof() function converts a C-style string, passed as an argument to atol() function, to double. It converts the C-string str to a value of type double by interpreting the characters of the string as numerical values. It discards the leading whitespace characters until a non-whitespace character is found.

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 double value type representation of the string.
• The function returns zero (0.0) if no conversion is performed.

**Note: If the C-string str passed to atol() function is either empty or contains only whitespace characters, it is not a valid floating point number, no conversion will be performed and it will return 0.0.

Example: Program to Illustrate the Working of atof() Function.

C++ `

// CPP program to illustrate // working of atof() 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;

}

C

// C program to illustrate // working of atof() function. #include <stdio.h> // Include this header for atof function #include <stdlib.h>

int main() { // char array char pi[] = "3.1415926535";

// Calling function to convert to a double
double pi_val = atof(pi);

// prints the double value
printf("Value of pi = %lf\n", pi_val);

// 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
printf("Value of acceleration due to gravity = %.1lf\n",
       acc_g_val);

return 0;

}

`

Output

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