C++ string stof Function

C++ String stof

The std::stof function in C++ converts a string representation of a floating-point number into a float. Introduced in C++11 and defined in the <string> header.

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Syntax of string stof function

float stof(const std::string& str, std::size_t* idx = 0);

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Parameters of string stof function

Parameter	Description
str	The string containing the representation of a floating-point number.
idx (optional)	A pointer to a std::size_t object. If provided, it is set to the position of the first character in str after the numerical value. Defaults to 0.

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Return Value of string stof function

On successful conversion, std::stof returns the converted value as a float. If the conversion fails, it throws an exception.

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Exceptions for string stof function

The std::stof function can throw the following exceptions:

• std::invalid_argument: Thrown if the input string does not contain a valid floating-point number.
• std::out_of_range: Thrown if the converted value exceeds the range of the float type.

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Examples for string stof function

Example 1: Converting a Decimal String to Float

In this example, we convert a string containing a decimal number to a float using std::stof.

Program

#include <iostream>
#include <string>

int main() {
    std::string str = "123.456";
    float num = std::stof(str);
    std::cout << "The float value is: " << num << std::endl;
    return 0;
}

Output

The float value is: 123.456

Explanation

1. The program includes the necessary headers: <iostream> for input and output operations, and <string> for string handling.
2. A string str is initialized with the value "123.456", representing a decimal number.
3. The std::stof function converts the string to a float and stores it in the variable num.
4. The program outputs the float value using std::cout.

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Example 2: Converting a String with Leading and Trailing Whitespace to Float

In this example, we convert a string with leading and trailing whitespace to a float using std::stof.

Program

#include <iostream>
#include <string>

int main() {
    std::string str = "   789.012   ";
    float num = std::stof(str);
    std::cout << "The float value is: " << num << std::endl;
    return 0;
}

Output

The float value is: 789.012

Explanation

1. The string str contains the value " 789.012 ", with leading and trailing whitespace.
2. The std::stof function ignores the whitespace and successfully converts the string to a float.
3. The resulting float value is stored in num and printed using std::cout.

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Examples for Exception Handling in stof

Example 1: Handling std::invalid_argument

This exception is thrown when the string does not contain a valid numeric representation.

Program

#include <iostream>
#include <string>
#include <stdexcept>

int main() {
    std::string invalidStr = "abc123";
    try {
        float num = std::stof(invalidStr);
    } catch (const std::invalid_argument& e) {
        std::cout << "Invalid argument exception: " << e.what() << std::endl;
    }
    return 0;
}

Output

Invalid argument exception: stof

Explanation

1. The string invalidStr contains non-numeric characters, making it an invalid input for conversion to a float.
2. When std::stof is called, it throws a std::invalid_argument exception because the string does not represent a valid floating-point number.
3. The exception is caught in the catch block, and an appropriate error message is displayed using std::cout.

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Example 2: Handling std::out_of_range

This exception is thrown when the value represented by the string exceeds the range of the float type.

Program

#include <iostream>
#include <string>
#include <stdexcept>

int main() {
    std::string largeStr = "1e40"; // A number too large for float
    try {
        float num = std::stof(largeStr);
    } catch (const std::out_of_range& e) {
        std::cout << "Out of range exception: " << e.what() << std::endl;
    }
    return 0;
}

Output

Out of range exception: stof

Explanation

1. The string largeStr contains the value "1e40", which represents a number that exceeds the range of the float type.
2. When std::stof is called, it throws a std::out_of_range exception because the value is too large to be represented as a float.
3. The exception is caught in the catch block, and an appropriate error message is displayed using std::cout.