code on infinte loop: start of a jpg UPDATE

Question

I've some issues with my code, it compiles but it gets stuck in an infinite loop. I've run gdb and apparently it never finds the start of a jpg.

here is a snippet:(UPDATE here is the rest of the code)

I changed the fread in the while loop for fgetc but it is still running forever

int main(int argc, char* argv[]) { if (argc != 1) { printf("executing should not have additional input!"); }

FILE* inptr = fopen("card.raw", "r");
bool jpeg = false;
int found = 0;
int position = 0;
BYTE data[512];
char title[8];
FILE* image;

while (fgetc(inptr) != EOF)    {

// reads the file and checks if it is the beginning of a jpeg   

fread(&data, 512, 1, inptr);
    if(data[0] == 0xff && data[1] == 0xd8 && data[2] == 0xff && (data[3]==0xe0 || data[3]==0xe1))
            {

                        jpeg = true;
                        found += 1;
                    }


if (jpeg == true)
{
    //it only executes once it has found a new jpeg
    if (position == found -1)
    {
        fclose(image);
        if (found <= 10)
            {                
            sprintf (title, "00%d.jpg", found-1);
            image = fopen(title, "w");
            }
        else
            {
            sprintf (title, "01%d.jpg", found-11);
            image = fopen(title, "w");
            }        

        position ++;
    }

    fwrite(&data, 512, 1, image);

}

}

//closing files fclose(inptr); fclose(image);

//the end
return 0;

}

Answer 1

You are reading two 512 byte blocks of data before you do anything with them, so every odd block of data is simply thrown away (or worse, depending on the rest of the code.) If all of the signatures fall on odd numbered blocks, it's possible that you would never see them. Or, there could be something else wrong in the code that we haven't seen.

while (fread(&data, 512, 1, inptr) == 1) {
fread(&data, 512, 1, inptr);

As for the loop, there's no telling what's going on without seeing the rest of the while loop code.