Question

I have 2 loops:

//Loop 1
for ( vector<string>::iterator iter = vecv.begin() ; iter != vecv.end()  ; iter++)
    {
        cout << "-----IN LOOP----" <<  *iter;
    }

//Loop 2
for ( vector<string>::iterator iter = vecv.begin() ; iter != vecv.end()  ; iter++)
    {
        cout << "-----IN LOOP----" <<  *iter << endl ;
    }

Now vecv is a string vector and contains 2 strings:

65 and A000 respectively.

Now the loop 1 Does not print anything, in fact the loop seems to not run at all.

However on adding the endl as you see in Loop 2, it gives this output:

-----IN LOOP----65
-----IN LOOP----$A000

What is happening exactly?

Mind you i am facing this problem only in Visual Studio 2010 and not Dev-C++!!

Answer 1

How do you know it doesn’t print anything without endl? By observing running program? If so, the problem is that cout provides buffered output: it actually prints somehting on the screen (or in the file) only when its buffer is full.

endl on other hands flushes the buffer.

If you want unbuffered output you can use cerr, but it would lead to some differences (like, now if you want to redirect output to file you should do 2> instead of > etc.)

If you want buffered output but don’t want to have newlines, print flush into cout.