whodunit

Questions

What's stdint.h?

stdint.h is a header file for instroducing more integer datatypes which allows to be more precise as to what width the datatype can be, for example, integer can be unsigned, signed with size of width 8 bits, 16, 32, and maximum up to 64 bits.

What's the point of using uint8_t, uint32_t, int32_t, and uint16_t in a program?

This are the C/C++ aliases of primitive data types that map to data types used in Windows programming like BYTE, DWORD, LONG, and WORD.

How many bytes is a BYTE, a DWORD, a LONG, and a WORD, respectively?

• BYTE: 1 byte
• DWORD: 4 bytes
• LONG: 4 bytes
• WORD: 2 bytes

What (in ASCII, decimal, or hexadecimal) must the first two bytes of any BMP file be? Leading bytes used to identify file formats (with high probability) are generally called "magic numbers."

First two bytes are: 0x4d42.

What's the difference between bfSize and biSize?

bfSize is total size of FILE in bytes, whereas biSize is total number of bytes required by the structure.

What does it mean if biHeight is negative?

If biHeight is positive, the bitmap is a bottom-up DIB and its origin is the lower-left corner. If biHeight is negative, the bitmap is a top-down DIB and its origin is the upper-left corner.

What field in BITMAPINFOHEADER specifies the BMP's color depth (i.e., bits per pixel)?

biBitCount (number of bits-per-pixel) field in the BITMAPINFOHEADER struct determines the number of bits that define each pixel and the maximum number of colors in the bitmap.

Why might fopen return NULL in lines 24 and 32 of copy.c?

fopen can return NULL if OS cannot open the file with given permission and type of mode, or filepath is invalid, or file is write-protected, in those cases fopen will return the NULL pointer.

Why is the third argument to fread always 1 in our code?

Because there's only one file and info header, and we read and write one RGBTRIPLE at a time.

What value does line 65 of copy.c assign to padding if bi.biWidth is 3?

$$ padding\ &=\ (4\ -\ (bi.biWidth\ *\ sizeof(RGBTRIPLE))\ %\ 4)\ %\ 4 \\ &=\ (4\ -\ (3\ *\ 3)\ %\ 4)\ %\ 4 \\ &=\ 3\ %\ 4 \\ $$

What does fseek do?

fseek is file position indicator which jumps over to offset specified from designated position - i.e. current position, beginning of file or end of file.

What is SEEK_CUR?

• SEEK_CUR : is the current position in file.

Whodunit?

It was Professor Plum with the Candlestick in the library.