Question

I have been creating a gtk+ application in eclipse. At a point in the code, an alert dialogue is displayed using code similar to the gtk+ hello world. When I run this program, the dialogue ends up displaying the content of ‘words’ as expected, but the program crashes when I close the dialogue. I am new to c, so I ran the program with debug expecting to find some simple mistake. However, when i ran with debug, the dialogue displayed ‘words’ preceded by many null characters and logged the message.

Pango-WARNING **: Invalid UTF-8 string passed to pango_layout_set_text()

This new problem is confusing, and to add to the confusion, the program also did not crash when the dialogue was closed.

In summary, when I run the code, the text is fine, and the program crashes. When I debug the code, the text is invalid, and the program does not crash.

The text in the dialogue is generated with the following code:

char*  answerBuffer = (char*)malloc(strlen(s)+strlen(words)+1);

strcat(answerBuffer,words);

char*  answer = (char*)malloc(strlen(answerBuffer)+1);
g_strlcpy(answer,answerBuffer,strlen(answerBuffer)+1);

return answer;

as the code executes, the length of answerBuffer is 320 and words is a char* argument set to “a,b,c,d”. I am running this on windows xp through eclipse with the minGW compiler using gtk+ 2.24. Can anyone tell me how to debug/fix this?

ps. ‘s’ contains text from a file followed by either one or twelve null characters (one if I run, twelve if I debug)

Answer 1

Given the code you’ve supplied, this line is the problem:

strcat(answerBuffer,words);

Why? Because you don’t know what is in answerBuffer. Malloc doesn’t necessarily zero memory it returns to you, so answerBuffer contains essentially random bytes. You need to zero at least the first byte (so it looks like a zero length string), or use calloc() to allocate your buffer, which gives you zeroed memory.