C program to merge two given image files binary based ppm files P6

Write a C program to merge two given binary-based ppm files (P6). The names of the two given
image files and the name of the combined image file are given as command line arguments. The
combined image is obtained by putting the second image to the top-right corner of the first
image. The sizes of the given image files are not fixed. If the width or the height of the first
image is less than that of the second, your program should report error.
All these image files can be opened with image viewer tools that can work with ppm file format.
For simplicity, the following restrictions are added to the file format of the input:
• no comment line after the file type specification
• width (number of columns) and height (number of rows) formatted as ASCII decimal in
the second line
• maximal value of color components given in the third line
This is a practice on using System Call I/O. You are not allowed to use standard I/O library
functions or other graphics related libraries.
Sample input (firework.ppm and 150.ppm):

Answer:

#include <fcntl.h>
#include <unistd.h>

int main(int argc, char *argv[]){
	long int fd1width=0,fd1height=0, fd2width=0,fd2height=0;
	char buf;
	int width=0, height=0, p=0;

	int fd1 = open (argv[1],O_RDONLY);	// open fd1
	int fd2 = open (argv[2],O_RDONLY);	// open fd2
    int fd3 = open(argv[3],O_WRONLY | O_CREAT | O_TRUNC,0755);	// open/create fd3

    // fd1
	do{	//reads first line
		read(fd1,&buf,1);
	}while(buf != '\n');

	while (buf < '0' || buf > '9') //ignores any whitespace
		read(fd1,&buf,1);

	while (buf >= '0' && buf <= '9'){	//getting width of fd1
		fd1width*=10;
		fd1width+=(buf-'0');
		read(fd1,&buf,1);
	}

	while (buf < '0' || buf > '9') //ignores any whitespace
		read(fd1,&buf,1);

	while(buf != '\n'){	//getting height of fd1
		fd1height*=10;
		fd1height+=(buf - '0');
		read(fd1,&buf,1);
	}

	while (buf < '0' || buf > '9') // ignores any whitespace
		read(fd1,&buf,1);

	while(buf != '\n')  // reads the max value of color
		read(fd1,&buf,1);

	// fd2
	do{	//skip first line
		read(fd2,&buf,1);
	}while(buf != '\n');

	while (buf < '0' || buf > '9')
		read(fd2,&buf,1);

	while (buf >= '0' && buf <= '9'){	//getting width of fd2
		fd2width*=10;
		fd2width+=(buf-'0');
		read(fd2,&buf,1);
	}

	while (buf < '0' || buf > '9') 
		read(fd2,&buf,1);

	while (buf != '\n'){	//getting height of fd2
		fd2height*=10;
		fd2height+=(buf-'0');
		read(fd2,&buf,1);
	}

    while (buf < '0' || buf > '9')  
		read(fd2,&buf,1);

	while(buf != '\n')  // reads the max value of color
        read(fd2,&buf, 1);

	lseek(fd1,0,SEEK_SET);	//set fd1 pointer back to the beginning
    //copy the first 3 line of fd1 to fd3
	while (p != 3){
		read(fd1,&buf,1);
		write(fd3,&buf,1);
		if (buf == '\n') 
			p++;
	}

	int px1[fd1width][fd1height];
	while(width < fd1width && height < fd1height){    //read fd1 and store in px1
		read(fd1,&px1[width][height],3);
		width++;

		if (width == fd1width){
			width = 0;
			height++;
		}
	}

	// reset width, height
	width = 0;
	height = 0;

	int px2[fd2width][fd2height];
	while (width < fd2width && height < fd2height){	//read fd2 and store px2
		read(fd2,&px2[width][height],3);
		width++;

        //start new line
		if (width == fd2width){
			width = 0;
			height++;
		}
	}
	// reset width, height
	width = 0;
	height = 0;

	//copy fd1 and fd2 into fd3
	while (width < fd1width && height < fd1height){
        //copy fd2 to the top-right of fd3
		if (width >= (fd1width-fd2width-1) && height < fd2height){
            //copys an entire line of fd2
			for (int i = 0; i <= fd2width;i++){
				write(fd3,&px2[i][height],3);
			}
			//start next height
			width = 0;
			height++;
		}
		else{
            // copys fd1 into fd3
			write(fd3,&px1[width][height],3);
			width++;
		}

		//start new line
		if (width == fd1width){
			width = 0;
			height++;
		}
	}
	close(fd1);
	close(fd2);
	close(fd3);
	return 0;
}