Binary reading returning zero - c

Question

I'm trying to read a binary file and display its contents in the terminal, but this line of code:
size_t readed = fread(buffer, sizeof(buffer), positionX, file);
It is returning zero, so my loop is stopped, what is the suggestion to solve this problem?
buffer = Storage
sizeof(buffer) = Size File
positionX = 7918080 <-- Dynamic Pointer
file = File to read
Terminal output:
https://i.stack.imgur.com/i9pls.png
My complete code:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
if (argc < 2)
{
printf("Usage: Please insert the file to read\n");
return 1;
}
else
{
FILE *file;
file = fopen(argv[1], "rb");
//Cannot open file --> check pointer file after fopen
if (file == NULL)
{
printf("Cannot open file \n");
exit(0);
}
long positionX = ftell(file);
printf("Pointer at the beginning %ld\n", positionX);
fseek(file, 0, SEEK_END);
positionX = ftell(file);
rewind (file); // Sets the position indicator associated with stream to the beginning of the file
unsigned char buffer[positionX]; // o buffer deveria ser criado aqui depois de pegar a posição final
printf("Pointer at the End: %ld\n", positionX);
// Read the content --> it's always good to check the read value
// the third parameter was 1, it should be "position"
size_t readed = fread(buffer, sizeof(buffer), positionX, file);
printf("the size is %zu\n", readed); // decimal size_t ("u" for unsigned)
printf("the size is %zx\n", readed); // hex size_t
for(size_t i = 0; i < readed; i++) // usar readed como limite
{
printf("%x ", buffer[i]); // prints a series of bytes
}
}
}
Thanks

Answer 1

Your call to fread is incorrect:
size_t readed = fread(buffer, sizeof(buffer), positionX, file);
The second parameter is the size of each element to read, and the third is the number of elements. This means that you're attempting to read up to sizeof(buffer) * positionX bytes, but buffer isn't that big. As a result, you write past the end of the buffer triggering undefined behavior.
Since you're reading positionX individual characters, you want 1 for the member size:
size_t readed = fread(buffer, 1, positionX, file);