How to read output from ostream?

Question

[SOLUTION]

You can pass a stringstream into the paramater that takes an ostream. After that you can get the text that was set inside the stringstream by its str() funktion.

#include <sstream> ... { stringstream ss; print(ss); string text; text = ss.str(); // Handle text }

Given there's a function like this:

void print(ostream& stream) const;

How can I access the data that is written into the ostream?

I was thinking of interpreting it as a string:

string text; print( text ); // Interpret text

The reason is there's another function that has a pointer to an object as a parameter:

void append( *Data data );

And I must use the data objects print method to get at its data:

// This is a public function in the Data class void append( *Data data ) { string text; data->print( text ); // append data to this Data object }

I was trying to cast to a stringstream but that didn't work. I'm thinking if I could save the data to a file and then read it as workaround.

Tony Delroy · Accepted Answer · 2012-04-25 12:50:52Z

3

Instead of this...

string text; print( text );

...try this...

ostringstream text; print( text );

Then you can use the text written into "text".

answered Apr 25, 2012 at 12:50

Tony Delroy

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4 Comments

user1356190 Over a year ago

Hmm, it doesn't spit any error but how can I convert the ostringstream to a string? the << operator doesn't work. neither does the ostringstreams str member and niether any combination of get or getline().

Tony Delroy Over a year ago

@user1356190: how were you trying to use the str() member function? Will work ala std::cout << text.str() << '\n';

user1356190 Over a year ago

Oh I didn't realize it had a str() function! Looking at the link [link]cplusplus.com/reference/iostream/ostream it doesn't say anywhere. Anyway, I passed a stringstream as the paramater for ostream and then I converted it into a string with "text = ss.str()". It works perfectly, thank you!

Tony Delroy Over a year ago

@user1356190: You're welcome. BTW - ostream is the base class - modelling any output stream, many of which don't keep a record of their output as it's sent to a network or device and no longer needed locally. ostream doesn't have a str() member function. The derived class ostringstream adds one though - it exists precisely to let you capture stream output in a string. Because print() accepts an ostream by reference, any derived class can be passed in and work polymorphically.

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