std::string::data() in C++

The data() function writes the characters of the string into an array. It returns a pointer to the array, obtained from conversion of string to the array. Its Return type is not a valid C-string as no ‘\0’ character gets appended at the end of array.
Syntax:

const char* data() const;
char* is the pointer to the obtained array.
Parameters : None

• std::string::data() returns an array that is owned by the string. Thus, the caller must not modify or free the memory.
  Let’s take same example where ptr points to final array.
  
  

  ptr[2] = 'a';
  this will raise an error as ptr points to an array that
  is owned by the string, in other words ptr is now pointing
  to constant array and assigning it a new value is now not allowed.
  

• Return value of data() is valid only until the next call of a non-constant member function for the same string.
  Explanation :
  Suppose, str be the original string which is required to be converted in an array

  // converts str in an array pointed by pointer ptr.
  const char* ptr = str.data(); 
  
  // Bad access of str after modification
  // of original string to an array
  str += "hello"; // invalidates ptr
  
  // Now displaying str with reference of ptr
  // will give garbage value
  cout << ptr; // Will give garbage value
  

// CPP code to illustrate
// std::string::data()

#include <iostream>
#include <string>
#include <cstring>
using namespace std;

// Function to demonstrate data()
void dataDemo(string str1)
{
    // Converts str1 to str2 without appending
    // '/0' at the end
    const char* str2;
    str2 = str1.data();

    cout << "Content of transformed string : ";
    cout << str2 << endl;

    cout << "After data(), length: ";
    cout << strlen(str2);


}

// Driver code
int main()
{
    string str("GeeksforGeeks");

    cout << "Content of Original String : ";
    cout << str << endl;
    cout << "Length of original String : ";
    cout << str.size() << endl;

    dataDemo(str);

    return 0;
}

Output:

Content of Original String : GeeksforGeeks
Length of original String : 13
Content of transformed string : GeeksforGeeks
After data(), length: 13

Here, we can easily notice, both contents and length of original string and transformed array are same.
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