Read len bytes of a file at offset and write it to FILETIME

Question

Is there any possibility to read sth from a binary file when knowing only the size of the element that should be red and the offset (in hexa)?

For example, if I want to read a FILETIME variable of 8 bytes, that has offset 0x001C, how do I approach this is C or C++?

I tried

fseek(pFile, 0x001C, SEEK_SET);
FILETIME* temp =(FILETIME*) malloc(sizeof(FILETIME));
fscanf(pFile, "%d", *temp);

but it doesn't properly work, I don't know why.

Thanks

"It doesn't properly work" is not a useful problem description. — Sam Varshavchik, Mar 27 '21 at 16:30
You cannot use `fscanf` with a binary file. Or, you can but it doesn't make sense. — Antti Haapala -- Слава Україні, Mar 27 '21 at 16:33
Where do you make use of the size of the element during the read operation? — JaMiT, Mar 27 '21 at 16:46
NB: binary-search is not what you think, it is an algorithm to search in O(log(n)) a value in a sorted array, I removed it from the tags. If you want to learn more about it: https://en.wikipedia.org/wiki/Binary_search_algorithm — Antonin GAVREL, Mar 27 '21 at 16:52
Why are you using dynamic memory to allocate 1 instance of FILETIME. You could use a single variable instead (avoids memory leaks). Or you could use `std::vector` — Thomas Matthews, Mar 27 '21 at 17:27

Antonin GAVREL · Accepted Answer · 2021-03-27T16:44:33.070

3

You can set your offset with fseek, and then read len of bytes with fread:

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    FILE *file = fopen("read_bytes.c", "rb");
    size_t offset = 0x001C;
    size_t len = 8;

    fseek(file, offset, SEEK_SET);
    FILETIME* temp = malloc(sizeof(FILETIME));
    fread(temp, 1, len, file);
}

edited Mar 27 '21 at 16:44

answered Mar 27 '21 at 16:37

Antonin GAVREL

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Why do you memcpy with a hardcoded length if you already have the length in a variable? Why do you read in a buffer and then use memcpy instead of directly reading? – Devolus Mar 27 '21 at 16:41
I don't have the FILETIME header, it was to test it, I edited to remove the memcpy and stick to OP's question – Antonin GAVREL Mar 27 '21 at 16:42
`FILETIME` is a binary structure, so you can not print it with `%s`. – Devolus Mar 27 '21 at 16:44
Thank you! It seems that the problem was that I was using fscanf instead of fread. Thanks a lot – Miruna Teleasa Mar 27 '21 at 16:44

Read len bytes of a file at offset and write it to FILETIME

1 Answers1