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Overview

This code snippet shows how to use string streams to convert strings to numbers and vice versa. The sstream library provides a functionality similar to sscanf() and sprintf() in the standard C library. The three main classes of this library are istringstream, ostringstream, and stringstream. An ostringstream object can be used to write to a string, an istringstream object can be used to read from a string, and a stringstream object can be used for both input and output to a string. String streams provide a great help when conversions between strings and numbers are needed.

Note: In order to use this code, you need to install the Open C/C++ plug-in.

This snippet can be self-signed.

MMP file

The following libraries are required:

LIBRARY  libstdcpp.lib
LIBRARY  libc.lib
LIBRARY  euser.lib

Source file

#include <iostream>  
#include <sstream>  
#include <string>
 
using namespace std;
 
//template conversion functions that can be used 
//with different number types
 
template<typename T>
T ConvertStringToNumber(const string& str)  
{  
  istringstream ss(str);  
  T number = 0;  
   
  ss >> number;  
     
  if (ss.fail( )) 
    {
    throw invalid_argument("ConvertStringToNumber:" + str);
    }
     
  return number;  
}  
    
template<typename T> 
string ConvertNumberToString (const T number) 
{
  ostringstream ss;
  
  ss << number;
  
  return ss.str();
}
 
 
int main()
{
// -- converting with stringstream --  
  int m = 1;
  int n = 0;
  string s1 = "";
  string s2 = "123";
  
  stringstream ss;
  
  //number to string
  ss << m;
  s1 = ss.str();
  cout << "s1:" << s1 << endl;  //s1:1
  
  //clear/reuse stringstream object
  ss.str("");
  
  //string to number
  ss << s2;
  ss >> n;  
  cout << "n:" << n << endl;  //n:123
  
// -- converting with istringstream and ostringstream --  
  try
    {  
    string intString = ConvertNumberToString<int>(1234);  
    cout << intString << endl; //1234
    
    string floatString = ConvertNumberToString<float>(1.2);  
    cout << floatString << endl; //1.2
    
    float floatVar = ConvertStringToNumber<float>(floatString);        
    cout << floatVar << endl; //1.2
        
    int intVar = ConvertStringToNumber<int>(intString);  
    cout << intVar << endl; //1234
        
    string exceptionString = "xyz";  
    intVar = ConvertStringToNumber<int>(exceptionString);  
       
    //this line is never executed because of exception 
    cout << intVar << endl;        
    } 
  catch (const exception& e) 
    {
    cout << e.what() << endl; //ConvertStringToNumber:xyz
    }
      
  return 0; 
}

Note: There is a known bug in the current Open C++ plug-in that prevents this code snippet to compile when working with the gcce compiler. To fix this problem, open the file stdapis/stlport/stl/_sstream.c and find and replace the following line:

if((_M_str.size() - _M_str._M_stream_pos) >= __n)

with

if((_M_str.size() - _M_str._M_stream_pos) >= (size_t)__n)

Postconditions

Different string-to-number and number-to-string conversions have been executed and are displayed as standard output. Exceptions have been caught because of an invalid conversion argument.

See also

• CS000891 - Converting C strings to numbers
• CS000897 - Converting numbers to C strings