Strange behavior with getline C++

Question

I am writing a simple program, where all the 'spaces' will be replaced by '%20'.

#include <iostream> #include <string> using namespace std; int main (int argc, char* argv[]){ string input; cout << "please enter the string where spaces will be replaced by '%20'" << endl; getline(cin, input); //count the number of spaces int countSpaces = 0; for (int i = 0 ; i < input.length() ; i++){ if (input[i] == ' '){ countSpaces++; } } int size = input.length() + (2 * countSpaces) + 1; //char cstr1[size]; char *cstr1 = new char[size]; char *cstr = cstr1; for (int i = 0 ; i < input.length() ; i++){ if(input[i] == ' '){ *cstr++ = '%'; *cstr++ = '2'; *cstr++ = '0'; } else{ *cstr++ = input[i]; } } *cstr == '\0'; cout << cstr1 << endl; delete[] cstr1; return 0; }

I get the following strange behavior:

With the test input "this is strange " I get "this%20is%20strange%20%20his is" , where I just expect "this%20is%20strange%20%20"
If I hard code the same string, I get the correct results.
Replacing char *cstr1 = new char[size]; with char cstr1[size]; & removing the delete[] while still fetching the input via getline also removes the error.

I am using i686-apple-darwin10-g++-4.2.1:

Any help is much appreciated.

Did you try stepping through the code in a debugger to see what is actually going on in the second loop ? — Paul R
– Paul R, Commented Jan 24, 2012 at 9:12

xpapad · Accepted Answer · 2012-01-24 09:13:22Z

6

The last line must be *cstr = '\0'; not ==

answered Jan 24, 2012 at 9:13

xpapad

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3 Comments

Paul R Over a year ago

Good catch - note also that if the OP had compiled with g++ -Wall ... the compiler would have caught the error for him.

shiraz Over a year ago

Thanks, it solved the problem. Looks like I am sleep deprived :P

Ulterior Over a year ago

These are the times I would like to slap my compiler too

Bob Kaufman · Accepted Answer · 2012-05-17 15:29:55Z

2

Change the *cstr == '\0'; in the end of your code to *cstr = '\0';
Violà!

edited May 17, 2012 at 15:29

Bob Kaufman

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answered Jan 24, 2012 at 9:14

Roee Gavirel

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Comments

Mooing Duck · Accepted Answer · 2012-05-17 16:13:30Z

 *cstr == '\0';

this line checks if *cstr is equal to '\0' or not and return 1 or 0 accordingly

that is wrong as you want to insert the \0 character at the end of the string so write single = instead of double =

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