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My implementation of CS50x Pset4 - Whodunit
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/**************************************************************************** | |
* whodunit.c | |
* | |
* HarvardX - CS50 | |
* Problem Set 4 | |
* | |
* Change the colour of a BMP's pixels to reveal a hidden message | |
***************************************************************************/ | |
#include <stdio.h> | |
#include <stdlib.h> | |
#include "bmp.h" | |
int main(int argc, char *argv[]) | |
{ | |
// ensure proper usage | |
if (argc != 3) | |
{ | |
fprintf(stderr, "Usage: ./whodunit infile outfile\n"); | |
} | |
// remember filenames | |
char *infile = argv[1]; | |
char *outfile = argv[2]; | |
// open input file | |
FILE *inptr = fopen(infile, "r"); | |
if (inptr == NULL) | |
{ | |
fprintf(stderr, "Could not open %s.\n", infile); | |
return 2; | |
} | |
// open output file | |
FILE *outptr = fopen(outfile, "w"); | |
if (outptr == NULL) | |
{ | |
fclose(inptr); | |
fprintf(stderr, "Could not create %s.\n", outfile); | |
return 3; | |
} | |
// read infile's BITMAPFILEHEADER | |
BITMAPFILEHEADER bf; | |
fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr); | |
// read infile's BITMAPINFOHEADER | |
BITMAPINFOHEADER bi; | |
fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr); | |
// ensure infile is (likely) a 24-bit uncompressed BMP 4.0 | |
if (bf.bfType != 0x4d42 || bf.bfOffBits != 54 || bi.biSize != 40 || | |
bi.biBitCount != 24 || bi.biCompression != 0) | |
{ | |
fclose(outptr); | |
fclose(inptr); | |
fprintf(stderr, "Unsupported file format.\n"); | |
return 4; | |
} | |
// write outfile's BITMAPFILEHEADER | |
fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, outptr); | |
// write outfile's BITMAPINFOHEADER | |
fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, outptr); | |
// determine padding for scanlines | |
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4; | |
// iterate over infile's scanlines | |
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++) | |
{ | |
// iterate over pixels in scanline | |
for (int j = 0; j < bi.biWidth; j++) | |
{ | |
// temporary storage | |
RGBTRIPLE triple; | |
// read RGB triple from infile | |
fread(&triple, sizeof(RGBTRIPLE), 1, inptr); | |
// change red pixels to white | |
if (triple.rgbtRed == 0xff) | |
{ | |
triple.rgbtRed = 0xff; | |
triple.rgbtGreen = 0xff; | |
triple.rgbtBlue = 0xff; | |
} | |
// write RGB triple to outfile | |
fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr); | |
} | |
// skip over padding, if any | |
fseek(inptr, padding, SEEK_CUR); | |
// then add it back (to demonstrate how) | |
for (int k = 0; k < padding; k++) | |
{ | |
fputc(0x00, outptr); | |
} | |
} | |
// close infile | |
fclose(inptr); | |
// close outfile | |
fclose(outptr); | |
// success | |
return 0; | |
} | |
/**************************************************************************** | |
* bmp.h | |
* | |
* BMP-related data types based on Microsoft's own. | |
***************************************************************************/ | |
#include <stdint.h> | |
/** | |
* Common Data Types | |
* | |
* The data types in this section are essentially aliases for C/C++ | |
* primitive data types. | |
* | |
* Adapted from https://msdn.microsoft.com/en-us/library/cc230309.aspx. | |
* See http://en.wikipedia.org/wiki/Stdint.h for more on stdint.h. | |
*/ | |
typedef uint8_t BYTE; | |
typedef uint32_t DWORD; | |
typedef int32_t LONG; | |
typedef uint16_t WORD; | |
/** | |
* BITMAPFILEHEADER | |
* | |
* The BITMAPFILEHEADER structure contains information about the type, size, | |
* and layout of a file that contains a DIB [device-independent bitmap]. | |
* | |
* Adapted from https://msdn.microsoft.com/en-us/library/dd183374(v=vs.85).aspx. | |
*/ | |
typedef struct | |
{ | |
WORD bfType; | |
DWORD bfSize; | |
WORD bfReserved1; | |
WORD bfReserved2; | |
DWORD bfOffBits; | |
} __attribute__((__packed__)) | |
BITMAPFILEHEADER; | |
/** | |
* BITMAPINFOHEADER | |
* | |
* The BITMAPINFOHEADER structure contains information about the | |
* dimensions and color format of a DIB [device-independent bitmap]. | |
* | |
* Adapted from https://msdn.microsoft.com/en-us/library/dd183376(v=vs.85).aspx. | |
*/ | |
typedef struct | |
{ | |
DWORD biSize; | |
LONG biWidth; | |
LONG biHeight; | |
WORD biPlanes; | |
WORD biBitCount; | |
DWORD biCompression; | |
DWORD biSizeImage; | |
LONG biXPelsPerMeter; | |
LONG biYPelsPerMeter; | |
DWORD biClrUsed; | |
DWORD biClrImportant; | |
} __attribute__((__packed__)) | |
BITMAPINFOHEADER; | |
/** | |
* RGBTRIPLE | |
* | |
* This structure describes a color consisting of relative intensities of | |
* red, green, and blue. | |
* | |
* Adapted from https://msdn.microsoft.com/en-us/library/dd162939(v=vs.85).aspx. | |
*/ | |
typedef struct | |
{ | |
BYTE rgbtBlue; | |
BYTE rgbtGreen; | |
BYTE rgbtRed; | |
} __attribute__((__packed__)) | |
RGBTRIPLE; |
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