to convert from string to integer

**vopo** · 02-13-2008

Hi,

I'm having some problems trying to change a string into an integer. I've looked up some examples, but can't seem to find the problem.

Here's my code:

Code:

#include <stdio.h> 
#include<iostream> 
#include<iomanip>
#include<sstream>
#include<fstream>
#include<string>
#include<cctype>

using std:: cout;
using std:: cin;
using std:: endl;
using namespace std;

void conversion(string& text);


int main()
{
	string textX = "234";
	conversion(textX);
	
	return 0;
}


void conversion(string& text)
{
	int number;
	number = atoi(text);
}

**laserlight** · 02-13-2008

The problem is that atoi() takes a const char*, not a std::string, as its argument.

Here is a simple example that uses a string stream for the conversion:

Code:

#include <iostream>
#include <string>
#include <sstream>

int main()
{
    std::string text("123");    // The string with the number.
    std::stringstream ss(text); // The string stream that is initialised with the string.
    int number;                 // The resultant number.
    ss >> number;
}

**h3ro** · 02-13-2008

atoi takes a c type string

Code:

#include <string>
#include <iostream>

using namespace std;

int main ()
{
  int i;
  string number = "321";

  i = atoi(number.c_str());
  
  cout << i;
  
  system("PAUSE");
  return 0;
}

**Elysia** · 02-13-2008

You might also want to replace atoi with strtol, since it's safer and better.

**Dino** · 02-13-2008

Up until recently, I too was also confused on how to convert an int or double into a string internally in a program to generate larger more complex strings that weren't destined for the user, and string streams are definitely the easy way to go.

Code:

 
#include <sstream> 
...
int abc = 123 ; 
char doremi[] = "do re mi" ; 
...
stringstream ss ; 

ss << "ABC, easy as... " << abc << ", simple as... " << doremi <<", baby it's you and me!"  ;

Todd (showing my age)

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