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Showing content from https://www.tutorialspoint.com/cpp_standard_library/cpp_string_stof.htm below:

C++ String to Float Conversion

The C++ std::string::stof() function is used to convert a string to a floating point number. This function analyse the string, extracting a floating point value starting from the beginning of the string. If the conversion is successful, it returns the float value, otherwise it throws an invalid_argument exception.

Following is the syntax for std::string::stof() function.

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

This function has two parameters as described below.

• str − It indicates the string object with the representation of a floating point number.
• idx − It indicates the pointer to an object of type size_t, whose value is set by the function to position of the next character in str after the numerical value.

This function returns the float value corresponding to the contents of the string passed as the argument.

Following is the basic example to convert a string into float of std::stof() function using C++.

#include <string>
#include <iostream>
using namespace std;
int main() {
   string temperature = " 36.6";
   float bodyTemp = stof(temperature);
   cout << "Body temperature is " << bodyTemp << " degree Celsius" << endl;
   return 0;
}

If we run the above code it will generate the following output.

Body temperature is 36.6 degree Celsius

Following is an another example passing a substring that contains a valid floating-point number, skipping the initial text.

#include <string>
#include <iostream>
using namespace std;
int main() {
   string mixedContent = "Height: 180cm";
   size_t pos;
   float height = stof(mixedContent.substr(7), & pos);
   cout << "Height = " << height << " cm " << endl;
   return 0;
}

If we run the above code it will generate the following output.

Height = 180 cm

In this example we are converting multiple numbers from a single string using string::stof in C++.

#include <string>
#include <iostream>
#include <vector>
using namespace std;
int main() {
   string data = "3.14 1.618 2.718";
   vector < float > numbers;
   size_t pos = 0, prev_pos = 0;
   while ((pos = data.find(' ', prev_pos)) != string::npos) {
      numbers.push_back(std::stof(data.substr(prev_pos, pos - prev_pos), nullptr));
      prev_pos = pos + 1;
   }
   numbers.push_back(stof(data.substr(prev_pos), nullptr));
   for (float num: numbers) {
      cout << num << std::endl;
   }
   return 0;
}

Following is the output of the above code.

3.14
1.618
2.718        

In this example we have given a invalid input, so it will throw an invalid_argument exception because the string cannot be converted to a float.

#include <string>
#include <iostream>
using namespace std;
int main() {
   string invalidNumber = "abc123";
   try {
      float value = stof(invalidNumber);
      cout << "Value is: " << value << std::endl;
   } catch (const invalid_argument & e) {
      cout << "Invalid argument: " << e.what() << endl;
   }
   return 0;
}

Following is the output of the above code.

Invalid argument: stof          

string.htm

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