ostringstream unexpected behaviour

[Old Wolf]

#include <iostream>
#include <ostream>
#include <sstream>

int main(void)
{
std:stringstream oss;

oss << "foo";

oss.str("APP");
std::cout << oss.str() << '\n';
oss << "END";
std::cout << oss.str() << '\n';

oss.str("");
oss << "APP";
std::cout << oss.str() << '\n';
oss << "END";
std::cout << oss.str() << std::endl;

return 0;
}

I expected to see the output:

APP
APPEND
APP
APPEND

but the second line said "END" instead. Why is this?
What is the best way to set the string in an ostringstream,
and leave it in a usable state?

 

[Victor Bazarov]

#include <iostream>
#include <ostream>
#include <sstream>

int main(void)
{
std:stringstream oss;

oss << "foo";

oss.str("APP");
std::cout << oss.str() << '\n';
oss << "END";
std::cout << oss.str() << '\n';

oss.str("");
oss << "APP";
std::cout << oss.str() << '\n';
oss << "END";
std::cout << oss.str() << std::endl;

return 0;
}

I expected to see the output:

APP
APPEND
APP
APPEND

but the second line said "END" instead. Why is this?
What is the best way to set the string in an ostringstream,
and leave it in a usable state?

Open the ostringstream for append (see ios_base::app).

Victor