I used fwrite() function to write 4 blocks of data into a file called "example2.bin". At the very beginning of the file, I also write the number of blocks (4 in this chase). Each block contains data in the following format: 0 (offset), 4 (size of the string), and the string "dang".
I first copied the memory address to char *buffer, which contains the number of blocks, and the 4 blocks of data as explained above. I then did the following:
filePtr = fopen("example2.bin", "wb+");
fwrite(buffer, contentSize, 1, filePtr); /*contentSize is the sum of the 4 blocks in byte */
The fwrite() worked well, and I was able to see the string saved in the file example2.bin. However, I have problem parsing the file example2.bin:
int main()
{
FILE *filePtr;
int listLength = 0;
int num_elements = 0;
int position = 0;
int offset = 0;
int size = 0;
char *data;
listLength = fileSize("example2.bin"); /* get the file size in byte */
filePtr = fopen("example2.bin", "rb");
fread(&num_elements, 1, 1, filePtr); /* get the number of blocks saved in this file */
printf("num_elements value is %d \n", num_elements);
position += sizeof(num_elements); /* track the position where the fread() is at */
printf("before the for-loop, position is %d \n", position);
int index;
for (index = 0; index < num_elements; index++)
{
fread(&offset, position, 1, filePtr);
position += sizeof(offset);
printf("offset is %d and position is %d \n", offset, position);
fread(&size, position, 1, filePtr);
position += sizeof(size);
printf("size is %d and position is %d \n", size, position);
fread(data, position, 1, filePtr);
position += size;
printf("size is %d and data is %s \n", size, data);
}
return 0;
}
When I run the compiled program, I got the following outputs, which is weird to me:
num_elements value is 4
before the for-loop, position is 4
offset is 0 and position is 8
size is 67108864 and position is 1996488708
Segmentation fault (core dumped)
I do not understand why the size and the position increased to such big numbers. I appreciate your help.