Read a file using "read()" function - c

Question

i'm studying C, and I need to read a text-file, but I can only use "write, malloc, free, open, read, close".
That's my code:
#define MAXCHAR 10000
int open_fp(int check)
{
char *int_vector;
int fp,len;
int i,j;
char buffer[MAXCHAR];
if(check == 0) //standard list
{
if((fp = open("file.txt", O_RDONLY)) != -1) //check if the fp is opened. -1 = error
{
printf("\n%d\n",fp); // DEBUG FUNCTION
sleep(1);
if (!(int_vector = (char*)malloc(sizeof(char) * sizeof(char))))
{
printf("\nWrong allocation\n!"); // DEBUG FUNCTION
return(0);
}
len = read(fp,int_vector,MAXCHAR);
for(i=0;i<len;i++)
{
printf("%c",int_vector[i]);
}
}
else
{
printf("File error!");
return (0);
}
}
return(0);
}
Now my question is: As you can read here,
char buffer[MAXCHAR];
i've created static buffer, but i would like create a dynamic buffer which allow me to resize the buffer according to the number of the chars in the text file, but i don't know how... someone have a trick😥😥 ?

Answer 1

First of all your way of allocating memory is wrong in below line.
//This allocates only 2 bytes of memory, but you are trying to read 10000
if (!(int_vector = (char*)malloc(sizeof(char) * sizeof(char))))
correct that line as below
//better to add one byte extra and store \0 at the end, useful in case of string operations
if (!(int_vector = malloc(MAXCHAR+1)))
and as far as your question is concerned, you dont need to reallocate memory in this particular case because you are just reading the bytes to buffer and printing.
a single malloc will suffice.
#include<stdlib.h>
#include<stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#define MAXCHAR 100
int open_fp(int check)
{
char *int_vector;
int fp,len;
int i,j;
char buffer[MAXCHAR];
if(check == 0) //standard list
{
if((fp = open("file.txt", O_RDONLY)) != -1) //check if the fp is opened. -1 = error
{
printf("\n%d\n",fp); // DEBUG FUNCTION
sleep(1);
if (!(int_vector = (char*)malloc(MAXCHAR)))
{
printf("\nWrong allocation\n!"); // DEBUG FUNCTION
return(0);
}
//not doing memset on purpose because only limited bytes are accessed.
while(len = read(fp,int_vector,MAXCHAR))
{
printf("\n **number of bytes read is %d **\n",len);
for(i=0;i<len;i++)
{
printf("%c",int_vector[i]);
}
}
printf(" At last LEN = %d\n", len);
//free the memory at the end
free(int_vector);
int_vector = NULL;
close(fp);// better to as fd
}
else
{
printf("File error!\n");
return (0);
}
}
return(0);
}
int main()
{
open_fp(0);
return 0;
}

Answer 2

ehm, If you forget to set realloc to it as well, here is some sample code for reallocation (dynamic resizing buffer)
#include <stdio.h>
#include <stdlib.h>
int main () {
char *str;
/* Initial memory allocation */
str = (char *) malloc(15);
strcpy(str, "tutorialspoint");
printf("String = %s, Address = %u\n", str, str);
/* Reallocating memory */
str = (char *) realloc(str, 25);
strcat(str, ".com");
printf("String = %s, Address = %u\n", str, str);
free(str);
return(0);
}