So I have a very simple program that reads the 3 first bytes of a file:
int main(void) { FILE *fd = NULL; int i; unsigned char test = 0; fd = fopen("test.bmp", "r"); printf("position: %ld\n", ftell(fd)); for (i=0; i<3; i++) { fread(&test, sizeof (unsigned char), 1, fd); printf("position: %ld char:%X\n", ftell(fd), test); } return (0); } When I try it with a text file it works fine:
position: 0 position: 1 char: 61 position: 2 char: 62 position: 3 char: 63
but when I run it with a PNG for example I get:
position: 0 position: 147 char:89 position: 148 char:50 position: 149 char:4E
Note that the 3 first bytes of the file are indeed 89 50 4E but I don't know where the 147 comes from. With a bmp file I get:
position: 0 position: -1 char:42 position: 0 char:4D position: 1 char:76
Do you know where these first positions come from? Thanks a lot for your help
