From String to const char pointer or char array and... back!

You can operate on strings in C++ both via the string class or the old (i.e. C like) const char pointer.

Notes on string:

To use the class string you have to include the string header:
#include <string>

In addition, to avoid mentioning every time the std namespace, I use the using keyword:

using namespace std;

(without this instruction you'll need to type std::string variable_name instead of just string variable_name)


From char* or char array to string

This is easier

const char *pCh="foo char* ";  // pointer to const char


/* two possible conversion methods */ 
string strTemp(pCh);    // through constructor
string strTemp= pCh;   // through assignment operator





NOTE:
Since the strong similarity between pointers and arrays, the previous commands work also with char arrays...



char aCh="foo char[] "; 

/* two possible conversion methods */ 
string strTemp(aCh);    // through constructor
string strTemp= aCh;   // through assignment operator






From string to char*or char array

In this case, the conversion to the const char is very quick, while going to char array takes a bit longer... 

string to const char*

string strMyString="This is a string";  // creation of a string object



/* using the c_str() method of the string object*/
const char *pCh=str.MyString.c_str(); 


string to char array

/ *
In this case, we need:
 (1) to assign the correct size of the char array 
 (2) to copy the string to the char array (char after char or by using strncpy) 
 (3) a null character to terminate the char array.
*/

  
string strMyString="This is a string";  // creation of a string object with size = 16!


/* using the size() method of the string object*/
char aCh[str.MyString.size()+1]; // the +1 is for terminating the char array with '\0', size=17!

// copying via the string strncpy...
strncpy(aCh, strMyString.c_str(), strMyString.size()); // SYNTAX: strncpy(destination, source, length)
 

// ... alternatively we can copy using a for loop:

for (int ii=0; ii<strMyString.size(); ii++)
     aCh[ii]=strMyString[ii];    //the loop stops at 15 and that's fine... we have copied 16 characters, since we started from 0!



// either way you use to copy the string, do not forget to add the null terminating character!


aCh[strMyString.size()]='\0';   // at position 16 in the char array

NOTE:
The trickiest part is always to take into account for the correct size of the char array, paying attention to the fact that in C/C++ arrays start at 0, not 1!!!