std::basic_string::c_str(3)

NAME
std::basic_string::c_str - std::basic_string::c_str

Synopsis
   const CharT* c_str() const; (noexcept since C++11)
                        (constexpr since C++20)
   Returns a pointer to a null-terminated character array with data equivalent to those
   stored in the string.
   The pointer is such that the range [c_str(), c_str() + size()] is valid and the
   values in it correspond to the values stored in the string with an additional null
   character after the last position.
   The pointer obtained from c_str() may be invalidated by:
     * Passing a non-const reference to the string to any standard library function, or
     * Calling non-const member functions on the string
       , excluding operator[], at(), front(), back(), begin(), rbegin(), end() and
       rend()
       (since C++11).
   Writing to the character array accessed through c_str() is undefined behavior.
   c_str() and data() perform the same function. (since C++11)

Parameters
   (none)

Return value
   Pointer to the underlying character storage.
   c_str()[i] == operator[](i) for every i in [0, size()). (until C++11)
   c_str() + i == std::addressof(operator[](i)) for every i in (since C++11)
   [0, size()].

Complexity
   Constant.

Notes
   The pointer obtained from c_str() may only be treated as a pointer to a
   null-terminated character string if the string object does not contain other null
   characters.

Example
// Run this code
 #include <algorithm>
 #include <cassert>
 #include <cstring>
 #include <string>
 extern "C" void c_func(const char* c_str)
 {
     printf("c_func called with '%s'\n", c_str);
 }
 int main()
 {
     std::string const s("Emplary");
     const char* p = s.c_str();
     assert(s.size() == std::strlen(p));
     assert(std::equal(s.begin(), s.end(), p));
     assert(std::equal(p, p + s.size(), s.begin()));
     assert('\0' == *(p + s.size()));
     c_func(s.c_str());
 }

Output:
 c_func called with 'Emplary'

See also
   front accesses the first character
   (DR*) (public member function)
   back accesses the last character
   (DR*) (public member function)
   data returns a pointer to the first character of a string
         (public member function)