Thread: Some help with realloc

Hi all, I'm new to C after working with PHP and other languages for years. I'm taking a class and having some problems with an assignment. In the following code, everything works fine until I try to realloc a size of 100. Then I get an "invalid next size" error. Any suggestions?

Code:

//CS306 Lab 1 lab1.c
//Author: Chris Wiegman
//Will search through file or
//standard input for a given string
//
//Call as:
// mygrep STRING [FILE...]
//Based on:
// Solution to Lab #1 in CS 306, Fall 2008
// Author: Norman Carver


#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#define FILE_BUFFER_SIZE 1024
#define INIT_BUFF_SIZE 50
#define INC_BUFF_SIZE 10

char *get_next_line(int fd);
int get_next_char(int fd);
int grep_open_file (char *search_string,int fd,char *file_pathname, int print_file);

int main(int argc, char *argv[]) {
	char *needle, *file_pathname;
	int i, fd, status = EXIT_SUCCESS;

	if (argc < 2) {
		fprintf(stderr,"Usage: mygrep STRING [FILE...]\n");
		return EXIT_FAILURE;
	}

	needle = argv[1];

	if(argc == 2) {
		file_pathname = "stdin";
		fd = 0;
		grep_open_file(needle,fd,file_pathname,0);
	} else {
		for (i=2; i<argc; i++) {
			file_pathname = argv[i];
			fd = open(file_pathname,O_RDONLY);
			if (errno > 0) {
				fprintf(stderr,"%s: Error opening file %s: %s\n", argv[0], file_pathname, strerror(errno));
				status = EXIT_FAILURE;
			} else {
      			grep_open_file(needle,fd,file_pathname,argc>3);
      			close(fd);
      		}
		}
	}
  return status;
}

int grep_open_file(char *needle, int fd, char *file_pathname, int print_file) {
	char *haystack;

    while ((haystack = get_next_line(fd)) != NULL) {
    	if (strstr(haystack,needle) != NULL) {
    		if (print_file) {
    			printf("%s:%s\n",file_pathname,haystack);
    		} else {
    			printf("%s\n",haystack);
    		}
    	}
    }

    if (errno > 0) {
    	fprintf(stderr,"Error reading from file %s: %s\n", file_pathname, strerror(errno));
    	return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}

char *get_next_line(int fd) {
	static char *line_buff;
	char *temp_buff;
	int buff_pos, next_char, chars_left, buff_size;
	static int string_complete;

	if (string_complete == 1 && line_buff == NULL) {
		free(line_buff);
	}

	buff_size = INIT_BUFF_SIZE;
	chars_left = buff_size;
	line_buff = malloc(buff_size);

	buff_pos = 0;

	while ((next_char = get_next_char(fd)) != '\n' && next_char != EOF) {
		//printf("%s: %d\n","chars_left",chars_left);
		if (chars_left > 0) {
			chars_left--;
		} else {
			buff_size = buff_size + INC_BUFF_SIZE;
			printf("%d\n",buff_size);
			//printf("%s\n",line_buff);
			temp_buff = line_buff;
			line_buff = realloc(line_buff,buff_size);
			if (line_buff == NULL) {
				string_complete = 1;
				return NULL;
			}
			chars_left = INC_BUFF_SIZE;
		}
		line_buff[buff_pos++] = next_char;
	}

	line_buff[buff_pos] = '\0';
	string_complete = 1;

	if (next_char == EOF && (buff_pos == 0 || (errno > 0))) {
		return NULL;
	} else {
		return line_buff;
	}
}

int get_next_char(int fd) {
	static char char_buff[FILE_BUFFER_SIZE];
	static int char_count, bytes_left,pos;
	if (bytes_left == 0) {
		char_count = read(fd, char_buff, FILE_BUFFER_SIZE);
		bytes_left = char_count;
		pos = 0;
	}
	if (bytes_left != 0) {
		bytes_left--;
		return char_buff[pos++];
	} else {
		return EOF;
	}
}

You're getting a runtime error? I don't recognize invalid next size as a possible result from realloc. If it fails, you should just get a NULL pointer.

That's what I would have thought, but that's not what is happening. I've tried testing for null with some print statements, yet they never get executed.

Well: what OS are you on, and what does it say, exactly?

Got it. I removed

Code:

chars_left = INC_BUFF_SIZE;

and it seems to be working fine. Thanks all!