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quick question - string

Posted on 2005-04-23
Medium Priority
Last Modified: 2012-05-05
hello experts,

I'm very beginner in C++ so I need helpwith two problems.
problem 1:
I have non-void function which returs string:

string TestString(int Integer){
        return "test";

I declared function prototypes and everything works fine until I want to cout this string.

cout << TestString(1);

I want to make this function to read integer from 1-12 and return string  for example:
and so on...

problem 2:
how can I connect string and variable together and print it out. I what to make error message consist from string(text) and variables is it possible?


string errormesage = "here some text " AND variable AND " again some text";

thank you


Question by:Luxana
LVL 86

Accepted Solution

jkr earned 600 total points
ID: 13852337
The following code snippet addresses both of your questions:

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

string TestString(int Integer){
      return "test";

int main () {

cout << TestString(1).c_str() << endl;

int variable = 42;

stringstream errormessage;

errormessage << "here some text " << variable << " again some text";

cout << errormessage.str().c_str() << endl;

return 0;

To the 1st one, you need to call 'string::c_str()' to use the correct operator for 'cout', to the 2nd one, the most efficiant and flexible way to do the formatting you suggested is using a stringstream, as demonstrated above. You can use it just like any other stream and access the contents as shown when you're done.
LVL 10

Author Comment

ID: 13852367

thanks for help. I started using unix g++ compiler and everything is working there without c_str() and #include <sstream> . ANyway I will try your solution as soon as I get back  to windows because I definitely need to make sure that my program can be compiled with visual C++ as well.

thanks again
LVL 10

Assisted Solution

Sys_Prog earned 1000 total points
ID: 13852480
The first part should work without any changes

When u return a string object, actually a temporary string object gets cnstructed and is returned.
And every temporary object in C++ is implicitly const.
Hence, acually, the object that gets subsstituted in the cout << is a const string.

Now, << is actally an overloaded operator and the syntax  is

ostream& operator<<( ostream& os, const string& s );


Now, as u can see, the << operator expects a reference to an ostream type of object on its left hand side (i.e. cout in your case) and a reference to a const string on right hand side (thats the returned string object in your case)
Hence it should work perfectly fine and It does with GNU compiler, as per the C++ standards

Also, regadring your 2nd question, u will  have to use stringstream object as shown above
Below is a reference for the same



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LVL 15

Assisted Solution

efn earned 400 total points
ID: 13852625
As Amit implied, you shouldn't need to call the c_str function to put a string out to a stream.

Possibly your problem was that output to the stream does not appear until you send an endl as in jkr's example.  Writing a '\n' character might also work, but an endl should definitely work.  Until the program writes an endl, the output data sits in a buffer, but may not be visible on the output device or window.

If that's not the problem, I think we would need to see more code to advise you further.
LVL 10

Author Comment

ID: 13857546
thanks guys for help this fix the problem: #include <sstream> it is interenstig because g++ compiler get my code work without  preprocessor directive <sstream>. Sys_Prog  was right that I do not need to do any changes so I accept his answer && jrk's && efn as assist .

thanks again

LVL 10

Author Comment

ID: 13857562
oops I did accepts jrk's answer I will ask page editor to change it.


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