Problems with malloc and realloc - c

Question

Why do I get 0 bytes after a block of size 7 alloc'd error when I am still leaving space for '\0'?
I tried allocating and reallocating 7 bytes and kept the size variable going up by 5 so that there would always be at least 2 bytes left at the end when I add the null terminator, but I am still getting the valgrind error:
Invalid write of size 1:
0 bytes after a block of size 7 alloc'd
whenever I read or write to token, for example I get it on this line:
token[i] = read;
void parse_file(char file[]) {
char read = 0;
int size = 5;
char *token = NULL;
int i = 0;
FILE *fp = NULL;
token = malloc(7 * sizeof(char));
fp = fopen(file, "r");
if(fp == NULL) {
fprintf(stderr, "%s: No such file or directory\n", file);
free(token);
fclose(fp);
return;
}
read = fgetc(fp);
while(read != EOF) {
if(i == size) {
token = realloc(token, 7 * sizeof(char));
size += 5;
}
if(isalpha(read)) {
read = (char) tolower(read);
token[i] = read;
}
else {
if(isalpha(token[0])) {
token[i] = '\0';
put(token);
}
else {
free(token);
}
token = calloc(7,sizeof(char));
size = 5;
i = 0;
read = fgetc(fp);
continue;
}
read = fgetc(fp);
i++;
}
free(token);
fclose(fp);
}

Answer 1

the following proposed code:
cleanly compiles
eliminates unnecessary code/logic
performs the desired functionality
properly checks for errors
incorporates the comments to the OPs question
incorporates the comments to this answer
and now the proposed code: (EDITED)
#include <stdlib.h> // exit(), EXIT_FAILURE, realloc(), free()
#include <stdio.h> // FILE, fprintf(), fopen(), fgetc(), perror()
#include <ctype.h> // isalpha(), tolower()
#include <errno.h> // errno
#include <string.h> // strerror()
// prototypes
void parse_file(char fileName[]);
void parse_file(char fileName[])
{
int byteRead = 0;
size_t size = 0;
char *token = NULL;
size_t i = 0;
FILE *fp = NULL;
fp = fopen(fileName, "r");
if( !fp )
{
fprintf(stderr, "Can't open %s: %s\n", fileName, strerror(errno));
exit( EXIT_FAILURE );
}
while( (byteRead = fgetc(fp) ) != EOF )
{
char *temp = NULL;
if(i >= size)
{
temp = realloc(token, 7 + size );
if( !temp )
{
perror( "realloc failed" );
free( token );
fclose( fp );
exit( EXIT_FAILURE );
}
// implied else, realloc successful
size += 7;
token = temp;
}
if( isalpha(byteRead) )
{
byteRead = tolower(byteRead);
token[i] = (char)byteRead;
i++;
}
else if( i )
{
token[i] = '\0';
puts(token);
free( token );
i = 0;
size = 0;
}
}
free(token);
fclose(fp);
}