Thread: Dynamic memory problem

Hi, I'm trying to read in a text file and count the number of seperate words in each line of the file. The number of lines and the maximum line length is already known. The program compiles ok without any warnings, and it runs fine up untill the free(buffer) function where the program crashes and I get the message "DAMAGE: after Normal block (#45) at 0x00320A70". If I comment out the do-while loop then it runs right through to the end, so I'm assuming its the strtok() function thats causing the problem somehow, but I don't know why. Can anyone help?

Code:

	char *sep, *buffer;

	buffer = (char*)malloc((MaxLineLen + 1)*sizeof(char));
	i = 0;
	do{
		fgets(buffer,MaxLineLen, input);
		buffer[strlen(buffer) - 1] = '\0';
		//printf("%s\n", buffer);
		sep = strtok(buffer, " ");
		while(sep != NULL)
		{
			sep = strtok(NULL, " ");
			WordsPerLine[i]++;
		}
		i++;
	}while(i < LineCount);
	free(buffer);

I tried to compile your code and have bunch of errors. Post the whole code.

This isn't the WHOLE code, but its enough to work. I just noticed after compiling this version that the WordsPerLine array never gets incremented even though the while loop appeared to be ok when i was stepping through it with the debugger.

Code:

#include<stdio.h>
#include<stdlib.h>
#include<conio.h>
#include<string.h>

int main(void)
{
	FILE *input;
	char InName[] = {"input.txt"}, *buffer, *sep;
	int c = 0, LineCount = 1, MaxLineLen = 0, i = 0;
	int *WordsPerLine;

	if((input = fopen(InName, "r")) == NULL)
	{
		printf("\t*** ERROR : the file '%s' was not opened ***\n\n\n", InName);
		getch();
		return 0;
	}

	while(c != EOF)	//calculate number of lines and max line length
	{
		c = getc(input);
		i++;
		if(c == 10 || c == 13)	//LF or CR
		{
			LineCount++;
			MaxLineLen = i;
			i = 0;
		}
	}
	fclose(input);

	WordsPerLine = (int*)malloc((LineCount + 1)*sizeof(int));
	buffer = (char*)malloc((MaxLineLen + 1)*sizeof(char));
	for(i=0;i<LineCount;i++)
		WordsPerLine[i] = 0;

	input = fopen(InName, "r");
	i = 0;
	do{
		fgets(buffer,MaxLineLen, input);
		buffer[strlen(buffer) - 1] = '\0';
		sep = strtok(buffer, " ");
		while(sep != NULL)
		{
			sep = strtok(NULL, " ");
			WordsPerLine[i]++;
		}
		i++;
	}while(i < LineCount);

	for(i=0;i<LineCount;i++)
		printf("Line %d : %d\n", (i+1), WordsPerLine[i]);
	free(buffer);
	free(WordsPerLine);
	fclose(input);
	getch();
	return 0;
}

Just a comment on your logic.

An end of line is usually denoted by a CR/LF combo. Your code increments the linecount when it runs into EITHER of these char's. But there are TWO char's for every end of line, so your linecount in being incremented twice for each actual end of line.

Why do all this to count words in a line of text? After the first letter in a sentence, every space (ascii 32), will indicate another word has been passed over, will it not?

When a program runs, but then quits due to memory problems, you can be sure it's leaked or badly fragmented, memory. No doubt at all.

Adak

Thanks for your help, I see what you mean about the LF/CR thing, but when I run the program it counts the correct number of lines. Can I rely on it to work for all windows xp machines?

I have another question... is this the correct way to allocate and free memory for a 3 dimentional character array?

Code:

char ***words = NULL;

//allocate memory

words = (char***)malloc(NumberOfLines*sizeof(char**));
for(i=0 ; i<NumberOfLines ; i++)
	words[i] = (char**)malloc(WordsPerLine*sizeof(char*));
for(i=0 ; i<NumberOfLines ; i++)
	for(j=0 ; j<WordsPerLine ; j++)
		words[i][j] = (char*)malloc((WordLength + 1)*sizeof(char));

//free memory

for(i=0 ; i<NumberOfLines ; i++)
	for(j=0 ; j<WordsPerLine ; j++)
		free(words[i][j]);
for(i=0 ; i<NumberOfLines ; i++)
	free(words[i]);
free(words);

No I don't think so
Something more like:-

words = (char***)malloc(rows*columns*height*sizeof(char));