C++ type conversion notes

    //older version
    atoi( str.c_str() )
    //------------------------------------------//
    // C++11
    // string -> integer
    int i = std::stoi(s);

    // string -> float
    float f = std::stof(s);

    // string -> double
    double d = std::stod(s);
    //------------------------------------------//
    #include <sstream>
    // string -> integer
    std::istringstream ( str ) >> i;

    // string -> float
    std::istringstream ( str ) >> f;

    // string -> double
    std::istringstream ( str ) >> d;
    //------------------------------------------//
    // Boost's lexical_cast
    #include <boost/lexical_cast.hpp>
    #include <string>

    std::string str;

    try {
        int i = boost::lexical_cast<int>( str.c_str());
        float f = boost::lexical_cast<int>( str.c_str());
        double d = boost::lexical_cast<int>( str.c_str());
        } catch( boost::bad_lexical_cast const&amp;amp;amp; ) {
            // Error management
    }

    char* strtoch(string str){
        char *cstr = new char[str.length() + 1];
        strcpy(cstr, str.c_str());
        return cstr;
    }
    //------------------------------------------//
    std::string x = "hello world";
    const char* p_c_str = x.c_str();
    const char* p_data = x.data();

    char* p_writable_data = x.data(); // for non-const x from C++17
    char* p_x0_rw = &x[0];  // compiles if x is not const...

    //------------------------------------------//
    std::vector<char> cstr(str.c_str(), str.c_str() + str.size() + 1);
    // or
    std::string str;
    std::vector<char> writable(str.begin(), str.end());
    writable.push_back('\0');

    #include <stdlib.h>

    int atoi(const char *nptr);
    long atol(const char *nptr);
    long long atoll(const char *nptr);
    long long atoq(const char *nptr);

    // read the value as an ascii code
    char a = 'a';
    // to
    int ia = (int)a;
    // or
    int ia = a;
    // or
    int num = static_cast<int>(letter); // if letter='a', num=97
    //------------------------------------------//
    //convert the character '0' -> 0, '1' -> 1, etc
    char a = '4';
    int ia = a - '0'; // a - '0' is equivalent to ((int)a) - ((int)'0')

    int i = 49;
    char c = i; // c='1' 49=1
    char c = (char)i; // c='1' 49=1
    char c = '0'+i; // c='a' 48+49=97=a

    int i = 49;
    char buffer[33];
    char *c = itoa(i,buffer,10);
``
### [int to string](https://stackoverflow.com/questions/5590381/easiest-way-to-convert-int-to-string-in-c)

```cpp
    #include <string>

    int i = 49;

    std::string s = std::to_string(i);

    // or
    auto s = std::to_string(i);

    // or
    char *intStr = itoa(i);
    string str = string(intStr);

    // or

    #include <sstream>

    stringstream ss;
    ss << a;
    string str = ss.str();

    // or

    #include <sstream>

    template <typename T>
    std::string NumberToString ( T Number )
    {
       std::ostringstream ss;
       ss << Number;
       return ss.str();
    }
    // or
    #include <boost/lexical_cast.hpp>
    int num = 4;
    std::string str = boost::lexical_cast<std::string>(num);
```