C++ std::string Conversion to (const) char*


In order to get const char* access to the data of a std::string you can use the string's c_str() member function. Keep in mind that the pointer is only valid as long as the std::string object is within scope and remains unchanged, that means that only const methods may be called on the object.


The data() member function can be used to obtain a modifiable char*, which can be used to manipulate the std::string object's data.


A modifiable char* can also be obtained by taking the address of the first character: &s[0]. Within C++11, this is guaranteed to yield a well-formed, null-terminated string. Note that &s[0] is well-formed even if s is empty, whereas &s.front() is undefined if s is empty.

std::string str("This is a string.");
const char* cstr = str.c_str(); // cstr points to: "This is a string.\0"
const char* data = str.data();  // data points to: "This is a string.\0"
std::string str("This is a string.");

// Copy the contents of str to untie lifetime from the std::string object
std::unique_ptr<char []> cstr = std::make_unique<char[]>(str.size() + 1);

// Alternative to the line above (no exception safety):
// char* cstr_unsafe = new char[str.size() + 1];

std::copy(str.data(), str.data() + str.size(), cstr);
cstr[str.size()] = '\0'; // A null-terminator needs to be added

// delete[] cstr_unsafe;
std::cout << cstr.get();