Copying a file into char array dynamically - c

Question

I have code for copying a text file (not binary) into an array of chars.
I am trying to copy the contents of a .txt file into a char* array.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
bool is_not_binary(const void *data, size_t len)
{
return memchr(data, '\0', len) != NULL;
}
int main(void)
{
char* file_name="./bash_example.sh";
FILE *file = fopen (file_name, "r");
size_t size = 64;
const size_t line_size = 300;
char *mem = malloc(size);
if (mem == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
*mem = 0;
if (file != NULL && is_not_binary(file_name,line_size)) {
char* line = malloc(line_size);
while (fgets(line, line_size, file) != NULL) {
size_t total = strlen(mem) + strlen(line) + 1;
if (size < total) {
size_t newsize = (total & ~1U) << 1;
char *tmp = realloc(mem, newsize);
if (tmp == NULL) {
perror("realloc");
exit(EXIT_FAILURE);
}
mem = tmp;
size = newsize;
}
strcat(mem, line);
}
}
printf("%s",mem);
return 0;
}
But in my code I must specify a static size:
size_t size = 64;
const size_t line_size = 300;
I want to remove this and I want dynamic allocation, is it possible?
Actually it's static code, 64 and 300.

Answer 1

I coded up an example that makes use of fopen, fread, and the classic example doubling the buffer size as the content grows.
int main()
{
const size_t initial_size = 1024;
char* contents = (char*)malloc(initial_size);
size_t length = 0;
size_t allocated = initial_size;
FILE* file = fopen("./sbatch_example.sh", "r");
if (file)
{
while (1)
{
size_t remaining = allocated - length;
size_t result = 0;
if (remaining == 0)
{
contents = (char*)realloc(contents, allocated*2);
allocated = allocated*2;
remaining = allocated-length;
}
result = fread(contents+length, 1, remaining, file);
length += result;
if (result==0) /* EOF */
{
break;
}
}
}
if (file)
{
fclose(file);
file = NULL;
}
/* at this point, "contents" is your file data bytes
and "length" is the number of bytes copied into that array*/
/*optional: append a null char to the end of the buffer to make it easier for debugging and print statements */
contents = (char*)realloc(contents, length+1);
contents[length] = '\0';
free(contents);
return 0;
}

Answer 2

You can use ftell() to get the total length in advance and fread() to read a whole at one time as below.
FILE *fp = fopen("./sbatch_example.sh", "r");
if (fp) {
fseek(fp, 0, SEEK_END);
size_t size = ftell(fp);
rewind(fp);
char *mem = malloc(size+1);
size_t nr = fread(mem, size, 1, fp);
}