C++: Converting Strings and Numbers

× Note:   For examples of converting QString objects to standard strings and numbers in Qt, follow this link.

This page provides several examples of how to convert standard C++ string objects to numeric types, and vice versa. The examples include older functions inherited from C, as well as newer conversion functions introduced in C++11.



  • C++11: convert a std::string to an int:

    std::string someString = “55”;
    int myInt = stoi(someString);

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  • C++11: convert a std::string to a double:

    std::string someString = “98.6”;
    double bodyTemp = stod(someString);

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  • C++11: convert a std::string to a float:

    std::string someString = “105.9”;
    float theX = stof(someString);

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  • C++11: convert a number to a std::string:

    std::string myString = to_string(2345.89);

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  • Convert a std::string to an int:

    std::string someStr = “180”;
    int myInt = atoi(someStr.c_str());  // c_str() needed to convert C++ string to a C-string

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  • Convert a std::string to a float:

    std::string someStr = “789.34”;
    float myFloat = atof(someStr.c_str());  // c_str() needed to convert C++ string to a C-string