The C++ code below does int
to string
and a string
to int
conversions. Then, it repeats these steps again. The stringstream
to int
line stream1 >> i3;
is breaking the code. What am I missing here?
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main()
{
int i1 = 101;
int i2 = 202;
int i3 = 0;
string s1 = "";
string s2 = "";
stringstream stream1;
for (int i=0;i<2;i++)
{
//int to string
stream1.str("");
cout << "i1 " << i1 << endl;
stream1 << i1;
s1 = stream1.str();
cout << "s1 " << s1 << endl;
//int to string
cout << "i2 " << i2 << endl;
stream1.str("");
stream1 << i2;
s2 = stream1.str();
cout << "s2 " << s2 << endl;
//string to int
stream1.str("");
stream1.str(s2);
stream1 >> i3;
//line above causes s1 and s2 to get messed up during 2nd time in for loop
cout << "i3-- " << i3 << endl;
}
return 0;
}
One effective way to convert a string object into a numeral int is to use the stoi() function. This method is commonly used for newer versions of C++, with is being introduced with C++11. It takes as input a string value and returns as output the integer version of it.
A stringstream associates a string object with a stream allowing you to read from the string as if it were a stream (like cin). To use stringstream, we need to include sstream header file. The stringstream class is extremely useful in parsing input.
I tested your code and could reproduce the problem. I solved it inserting a .clear() before .str("")
Have a look here: How to reuse an ostringstream?
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main()
{
int i1 = 101;
int i2 = 202;
int i3 = 0;
string s1 = "";
string s2 = "";
stringstream stream1;
for (int i=0;i<2;i++)
{
//int to string
stream1.clear();
stream1.str("");
cout << "i1 " << i1 << endl;
stream1 << i1;
s1 = stream1.str();
cout << "s1 " << s1 << endl;
//int to string
cout << "i2 " << i2 << endl;
stream1.clear();
stream1.str("");
stream1 << i2;
s2 = stream1.str();
cout << "s2 " << s2 << endl;
//string to int
stream1.clear();
stream1.str("");
stream1.str(s2);
stream1 >> i3;
//line above causes s1 and s2 to get messed up during 2nd time in for loop
cout << "i3-- " << i3 << endl;
}
return 0;
}
The problem is that the stream's EOF flag is being set while extracting the integer (i.e. stream1.eof()
returns true
), but you never clear it. Inserting a call to stream1.clear()
after extraction fixes your issue.
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