Help .. Conversion Problems

Ok, this is really stupid and I'm kicking myself with the fact that I'm stuck on it. I'm prototyping a small program that moves back and forth though a directory of images by their number. Basically I just want to increase or decrease my integer Page_Num (which I have done here) then convert that number to a const char* array and append the file extension to it so that I can open the next file in sequence.

Code:

void page_forward(Fl_Widget*, void*)
    {
     test->uncache();           // Clear the image

     const char* buffer;        // String buffer

     Page_Num = Page_Num + 1;   // Increase the page count

     // String conversion here ....

     test = new Fl_GIF_Image(buffer);    //load the image cache

     img_butt->image(test);                    // assign the cache to the button

     window->redraw();                          // Force a redraw
    }

Thanks ...

I think you probably want sprintf() to use C syntax or C++ stringstreams.

Originally Posted by elad

I think you probably want sprintf() to use C syntax or C++ stringstreams.

Thanks, you put me on the right track. Here's what I come up with that works:

Code:

void page_forward(Fl_Widget*, void*)
    {
     test->uncache();                       // Clear the image

     const char*  buffer;                   // Const buffer
     char*        temp_buff;                //Char Buffer
     const char*  file_ext = ".gif";     //File Extension
     stringstream ss;

     Page_Num = Page_Num + 1;     // Increase the page count

     ss << Page_Num << file_ext;     //combine them in the stream

     string s = ss.str();     //convert to string
     sprintf(temp_buff, ss.str().c_str());     //convert to char array
     
     buffer = temp_buff;     //convert to const

     test = new Fl_GIF_Image(buffer);     //load the image cache
     img_butt->image(test);     // assign the cache to the button

     window->redraw();      // Force a redraw
    }

It works well, but uses a little more memory then I like. It's also kind of lengthy. Is there a more efficiant way of doing this?

Code:

void page_forward(Fl_Widget*, void*)
    {
     test->uncache();                       // Clear the image

     const char*  file_ext = ".gif";     //File Extension
     stringstream ss;

     Page_Num = Page_Num + 1;     // Increase the page count

     ss << Page_Num << file_ext;     //combine them in the stream

     test = new Fl_GIF_Image(ss.str().c_str());     //load the image cache
     img_butt->image(test);     // assign the cache to the button

     window->redraw();      // Force a redraw
    }

No need for all those conversions, just pass the stream's string's const char* to the function.

Wow! I didn't know you could pass a stream as a const. I'm going to have to pull out the book on that. Thanks for your help. Here's my final code:

Code:

void page_forward(Fl_Widget*, void*)  //## 
    {
     const char*   file_ext = ".gif"; // File extension
     stringstream  sstream;           // our string stream

     test->uncache();                 // Clear the image cache

     if (Page_Num < Max_Count_Images) //## Check and increment the image count
        {
         Page_Num = Page_Num + 1;     // Increase the page count
        }
     else Page_Num = 1;               //## or return it to one
     
     sstream << Page_Num << file_ext; // Add our items to the stream

     test = new Fl_GIF_Image(sstream.str().c_str()); // create a new instance and load the image cache
     img_butt->image(test);           // assign the cache to the button

     window->redraw();                // Force a redraw
    }

Man I wish I had known that some time ago...

Technically this:

Code:

foo(sstream.str().c_str());

is the same as this:

Code:

string str = sstream.str();
const char* buffer = str.c_str();
foo(buffer);

without all the extra temporary variables.

The c_str() string function returns a const char pointer to its contents.