Converting strings and numbers using string streams in Open C++

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Article Metadata
Tested with
Devices(s): Nokia 6220 Classic
Platform(s): S60 3rd Edition, FP2
Keywords: istringstream, ostringstream, stringstream, stringstream::str(), stringstream::fail()
Created: aknyman (03 Sep 2008)
Last edited: hamishwillee (05 Jul 2012)



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
//string to number
ss << s2;
ss >> n;
cout << "n:" << n << endl; //n:123
// -- converting with istringstream and ostringstream --
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)


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


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

This page was last modified on 5 July 2012, at 07:13.
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