CODEWITHSUNDEEP
c++processflushcout
Matthew
Matthew

Reputation: 3956

Automatic cout flushing

Good day,

I wrote a Java program that starts multiple C++ written programs using the Process object and Runtime.exec() function calls. The C++ programs use cout and cin for their input and output. The Java program sends information and reads information from the C++ programs input stream and outputstream.

I then have a string buffer that builds what a typical interaction of the program would look like by appending to the string buffer the input and output of the C++ program. The problem is that all the input calls get appended and then all the output calls get posted. For example, and instance of the StringBuffer might be something like this...

2
3
Please enter two numbers to add. Your result is 5

when the program would look like this on a standard console

Please enter two numbers to add. 2
3
Your result is 5

The problem is that I am getting the order of the input and output all out of wack because unless the C++ program calls the cout.flush() function, the output does not get written before the input is given.

Is there a way to automatically flush the buffer so the C++ program does not have to worry about calling cout.flush()? Similiar to as if the C++ program was a standalone program interacting with the command console, the programmer doesn't always need the cout.flush(), the command console still outputs the data before the input.

Thank you,

Upvotes: 7

Views: 5107

Answers (2)

Mario Corchero
Mario Corchero

Reputation: 5575

In case someone comes looking for a way to set cout to always flush. Which can be totally fair when doing some coredump investigation or the like.

Have a look to std::unitbuf.

std::cout << std::unitbuf;

At the beginning of the program.

It will flush at every insertion by default.

Upvotes: 7

eqzx
eqzx

Reputation: 5599

I can't guarantee that it will fix all of your problems, but to automatically flush the stream when you're couting you can use endl

e.g.:

cout << "Please enter two numbers to add: " << endl;

using "\n" doesn't flush the stream, like if you were doing:

cout << "Please enter two numbers to add:\n";

Keep in mind that using endl can be (relatively) slow if you're doing a lot of outputting

See this question for more info

Upvotes: 3

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