Thread: Mixing C and C++ IO. What extra syncing do I need ?

(Please ignore portability issues, as this is just for fun)

Code:

std::string InputUI(std::string msg="Input",int numchars=50)
{
    std::string command = "kdialog --inputbox \"" + msg + "\"";
    auto f = popen(command.c_str(),"r");
    char* ret = new char[numchars];
    fgets(ret,numchars,f);
    ret[numchars-1]='\0';
    std::string ret_str = std::string(ret);
    delete [] ret;
    return ret_str;
}

But If I call this function twice in a row...and cout the strings returned, they seem to output after the second one is returned, even when I use endl in between.
Other than that, this seems to work fine for me, but have I missed something obvious?

Interesting problem, I don't think this is being caused by the mixing of C-stdio and C++ streams but maybe something to do with how cout chains the output.

With the following calls

Code:

   cout << InputUI("Input", 1000) << " ";
   cout.flush();
   cout << InputUI("Input 2", 1000) << endl;

   cout << InputUI("Input", 1000) << InputUI("Input 2", 1000) << endl;

I got the following results when entering "This is a test.", "Does it work?" for the first two dialogs, and "bye!", "Good" for the second two.

This is a test. Does it work?

and then

Goodbye!

Also shouldn't the following line:

Code:

ret[numchars-1]='\0'

Actually be:

Code:

ret[strlen(ret)-1]='\0'

If you are trying to remove the trailing end of line character.

Jim

Originally Posted by jimblumberg

Actually be:

Code:

ret[strlen(ret)-1]='\0'

If you are trying to remove the trailing end of line character.

Ok.

Originally Posted by oogabooga

Shouldn't you be pcloseing the pipe?

Yes.. I should be.
(Why doesn't it get closed upon the end of the block, though ?)

Originally Posted by Elysia

Why use new when you can use a vector? This is not thread safe.

What happens to the vector's size after being filled, if I pass its address ?