Some File Operations in C

fileOps.c

//Open file for reading/writing
FILE *input, *output;

//open file for reading
if((input=fopen("input", "r"))== NULL){
	perror("fopen");
	exit(EXIT_FAILURE);
}
//open file for writing
if((input=fopen("output", "w"))== NULL){
	perror("fopen");
	exit(EXIT_FAILURE);
}

//read-write-etc
close(input); close(output);

//-------------------------------------------//

//xor file data byte by byte - assumes equal file size!!
void xor_data(FILE* input1, FILE* input2, FILE* output){
	int cur_byte1, cur_byte2;
	while(((cur_byte1 = fgetc(input1)) != EOF) && ((cur_byte2 = fgetc(input2)) != EOF)){
		fputc(cur_byte1 ^ cur_byte2, output);
	}
}

//-------------------------------------------//
//split a file into 4

#define COMMAND_SIZE 500
void split_file_into4(FILE *input, char * filename){
	unsigned long fileSize;
	unsigned long fileChunk;
        char syscommand[COMMAND_SIZE];
	if(input){
		fseek(input, 0, SEEK_END); //cursor at the end of the file
		fileSize = ftell(input);  //take the length of the file
	}
	fileChunk = fileSize/4;
	if (fileSize%4 != 0)
		fileChunk++;

	printf("The size of each file is %lu\n", fileChunk);
    
        //split the files with bash command
	sprintf(syscommand,"split --bytes=%lu --suffix-length=1 --numeric-suffixes %s chunk",fileChunk,filename);
	system(syscommand);
}