c_str() truncating string (randomly?)

**chris2306** · 01-09-2011

Hi, Im currently trying to write a program to model the "Weasel" evolution model, described here: Weasel program - Wikipedia, the free encyclopedia

This basically consists of setting a target phrase, then, starting from a completely random phrase, "evolving" that random phrase towards the target phrase
The program itself seem to work fine, but I'm having a bit of difficulty with my output. Im using FLTK for the GUI, which cant handle normal strings, but requires converting them via

Code:

exmplstr.c_str()

Im outputting a new phrase, in the form of a c-string every 0.01 seconds by appending it to a buffer, which is then output in a text box.
My problem is that, seemingly randomly, when I use c_str(), the original string will become truncated, but this only ever happens where there is a space (not always the first space either):

Str: "1 2 3 4 5 6 7 8 9 0 { }...etc" <-multiple spaces in string
C-str "1 2 3 4 5"

Since this seems to happen seemingly randomly, I am at a loss as to what it might be, and google wasn't much help!

The particular code that converts the strings and adds them to the buffer is here:

Code:

cout << "\nGen Num: " << gn;	e1.setphrases(e1.breed()); //Generates new phrases
	string o = "\n Best from generation "; 
	o.append(intstr(gn)); //Append Number of generations thus far
	o.append(" is: ");
	cout << e1.getHiScr(); //Get random phrase closest to target phrase
	o.append(e1.getHiScr()); //Append this to o
	
	cout << "\nNrm: " << o;   //Testing difference
	cout << "\n Cstr: " << o.c_str(); //between original and converted
	
	progress->value(e1.getScr(e1.getHiScr())); //Update progress bar
	
	phrsbuff->append(o.c_str()); //Convert string o created above to cstr, append to text buffer
	outputbox->buffer(phrsbuff); //Put buffer in output box
	outputbox->redraw(); //Refresh box
	outputbox->insert_position(outputbox->buffer()->length()); //Scroll output
	outputbox->show_insert_position();                                      //box down
	
	Fl::add_timeout(0.01, generate_cb);

Sorry to dump a big wall of text. Ill attach all the code, as its easier to see what I mean if you see the program running. Also, I'm using Quincy: Simple free C/C++ programming IDE for Windows as an editor and compiler
Thanks

Chris

**tabstop** · 01-09-2011

You can't have a 0-byte in a string, since that marks the end of your string. (Not the character '0', but the character '\0', i.e., with ascii value 0.) If your genetic mutation thing can create a string with a 0-byte in the middle, then you'll have to fix it.

**chris2306** · 01-09-2011

Originally Posted by tabstop

You can't have a 0-byte in a string, since that marks the end of your string. (Not the character '0', but the character '\0', i.e., with ascii value 0.) If your genetic mutation thing can create a string with a 0-byte in the middle, then you'll have to fix it.

Could you possibly elaborate on that please? The example I gave of the difference between the normal string and the converted string was pretty literal, I'm not sure why one space in the string would be case it to truncate and not one of the other spaces?

Ive been using " 1 2 3 4 5 6 7 8 9 0 - = [ ] ; ' # , . /" as a test target phrase, and the most recent run I did gave:

Normal String: ",1 2 3m4 5 6 7 8 q X - = [ ].C ' # f . /"
Converted: ",1 2 3m4 5 6 7 8 q X -"

Thanks for the quick reply

**tabstop** · 01-09-2011

If it was a space, you wouldn't have a problem. I'm guessing you have an actual \0 character, which is not at all like a space, really.

Are you still doing those debug print statements I see posted here? Is o short, or just o.c_str? If your strings are always supposed to be the same length, you could do

Code:

for (int k = 0; k < string_length; k++) {
    cout << static_cast<int> o[k] << " ";
}

to see the actual values of the characters.

**chris2306** · 01-09-2011

Originally Posted by tabstop

If it was a space, you wouldn't have a problem. I'm guessing you have an actual \0 character, which is not at all like a space, really.

Are you still doing those debug print statements I see posted here? Is o short, or just o.c_str? If your strings are always supposed to be the same length, you could do

Code:

for (int k = 0; k < string_length; k++) {
    cout << static_cast<int> o[k] << " ";
}

to see the actual values of the characters.

Yep I am, that was where I got these from:

Normal String: ",1 2 3m4 5 6 7 8 q X - = [ ].C ' # f . /"
Converted: ",1 2 3m4 5 6 7 8 q X -"

Thanks for the help, I will try what you suggest and see what I get

**chris2306** · 01-09-2011

Thanks so much

you were right, turns out the range of random numbers I was generating was one larger than my character dictionary, so every now and then it would reach outside it and get that \0 value

Thanks again for all your help!

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