Programming

glibc detected *** realloc(): invalid next size: 0x0804a170

#include <stdio.h>

main(int argc, char *argv[]) {
    FILE *fp;
    char *contents;    
    char *tmpptr;

    char buf[2];
    int fd;
    int i = 0;
    long lFileLen = 0;

    char fn[25];    
    fn[0] = '\0';
    
    if (argc < 2) {
    	printf("need argument.\n");
    	exit(1);
    }
    sprintf(fn, "/proc/%s/cmdline", argv[1]);
    
    fp = fopen(fn, "rb"); /* Open in BINARY mode */
    if (fp == NULL) {
        perror("could not open cmdine.");
        printf("path=[%s]\n", fn);
        exit(1);
    }

    contents = (char*) calloc(1, sizeof(char)); 
    
    fd = fileno(fp);
    while ((i = read(fd, buf, 1)) > 0) { /* read 1 char at a time */

     /* the contents of /proc/<pid>/cmdine has embedded null chars, so convert to ' ' */
          if (buf[0] == '\0') 
              buf[0] = ' ';

          lFileLen += i;
          tmpptr = (char*) realloc (contents, lFileLen * sizeof(char) + 1);  /* <<<--- what is wrong??? */

          if (tmpptr == NULL) {
             perror("Unable to realloc()");
             free(contents);
             exit(1);
          } else {
             contents = tmpptr;
          }
          strcat(contents, buf);   /* <<<--- this is related to the realloc() error message, but not sure why??? */
printf("###\n");
          
    } /* while ((i = read(fd, buf, 1)) > 0) */
    
   
    fclose(fp);
    
printf("total length: %ld\n", lFileLen);    
printf("content is [%s]\n", contents); 
printf("strlen: %d\n", strlen(contents)); 
    free(contents);
    free(tmpptr);
}

contents = (char *)realloc(contents, lFileLen * sizeof(char) + 1);

tmpptr = (char*) realloc (contents, lFileLen * sizeof(char) + 99);

strcat(contents, buf);   /* <---- why is this a problem */

tmpptr = (char *) realloc (contents, lFileLen * sizeof(char) + 1); /* your command */
contents = (char *)realloc(contents, lFileLen * sizeof(char) + 1); /* my suggestion in red */