Question

I want to read user input, something like here :

char *text  = new char[20] ;
cin >> text ;

but if the user enters “hello”, I want my other empty characters to be filled with space or -, something like:

"hello------------------------"

How can I do this?

Answer 1

There’s no standard and fast way to do this. I can think of some options.

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Suppose we have:

char *text  = new char[20];
cin >> text;

Note – we need to know that the capacity is 20! I’d recommend you to use some constant for this, especially if this will be used for other strings, too.

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Okay, first option – use std::stringstream

std::stringstream ss;
ss << setw( 20 - 1 ) << setfill( '-' ) << text;
//            ^^^^ we need one byte for the '\0' char at the end
ss >> text;

But this is rather slow.

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Fill the chars by hand:

int length = strlen( text );
for( int i = length; i < 20 - 1; ++i ) // again - "20-1" - '\0'
{
    text[ i ] = '-';
}
text[ 20 - 1 ] = '\0'; // don't forget to NULL-terminate the string

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And the best way, according to me – get rid of these char* things (you have tagged the question as c++ ) and just use std::string.

std::string sText;
std::cin >> sText;
sText.resize( 20, '-' ); // NOTE - no need to NULL-terminate anything

Voilà! (:

This way is much more clear and you don’t need to carry about using delete[] text; at the end (which is not that trivial sometimes, especially in case of some exception before delete[] – this will give you 100% memory leak. Of course, you can always use smart pointers.. but smart pointers for this?! 🙂 )

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Of course, you can write 19 instead of 20-1, I just wanted to “highlight” the -1, in case that you use some constant.