How to get a char* pointer to a C++ string?

Question

I have a C++ string. I need to pass this string to a function accepting char* parameter,

for example - strchr().

a) How do I get that pointer?

b) Is there some funtion equivalent to strschr() that works for C++ strings?

Answer 1

If str in your string use str.c_str() method to get the char* inside it.

Answer 2

1. To get the C string equivalent of the C++ string object use c_str function.
   
2. To locate the first occurence of a char in a string object use find_first_of function.

Example:

string s = "abc";

// call to strlen expects char *
cout<<strlen(s.c_str());  // prints 3

// on failure find_first_of return string::npos
if(s.find_first_of('a') != string::npos)
    cout<<s<<" has an a"<<endl;
else
    cout<<s<<" has no a"<<endl;

Note: I gave the strlen just an example of a function that takes char*.

Answer 3

Surprisingly, std:;string has far, far more capabilities than C-style strings. You probably want the find_first_of() method. In general, if you find yourself using the strxxx() functions on C++ std::strings, you are almost certainly doing something wrong.

Like much of the C++ Standard Library, the string class is a complex beast. To make the most of it, you really need a good reference book. I recommend The C++ Standard Library, by Nicolai Josuttis.

Answer 4

If you just want to assign a string literal to pw, you can do it like

char *pw = "Hello world";

If you have a C++ std::string object, the value of which you want to assign to pw, you can do it like

char *pw = some_string.c_str()

However, the value that pw points to will only be valid for the life time of some_string.

More here :
http://stackoverflow.com/questions/2235366/how-to-assign-a-string-to-char-pw-in-c

GoodLUCK!!

Answer 5

You can't get a char* from a string

string does not allow you free access to its internal buffer. The closest you can get is a const char* using .c_str() if you want it null terminated or .data() if it doesn't have to be null terminated.

You can then cast the pointer returned by these functions to char* but you do this on your own risk. That being said this is a relatively safe cast to make as long as you make sure you're not changing the string. If you changed it then the pointer you got from c_str() may no longer be valid.

This code:

string str("Hello World!");
char* sp = (char*)str.c_str();
sp[5] = 'K';

is probably ok
However this:

string str("Hello World!");
char* sp = (char*)str.c_str();
str = "Chaged string";
sp[5] = 'K';

is most definitely not ok.

Answer 6

std::string yourString("just an example");
char* charPtr = new char[yourString.size()+1];
strcpy(charPtr, yourString.c_str());

Answer 7

Perhaps this exmaple will help you

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

int main ()
{
  string str ("Replace the vowels in this sentence by asterisks.");
  size_t found;

  found=str.find_first_of("aeiou");
  while (found!=string::npos)
  {
    str[found]='*';
    found=str.find_first_of("aeiou",found+1);
  }

  cout << str << endl;

  return 0;
}