Remade cat using more system calls for better speed

src/cat.c

@@ -1,49 +1,51 @@
-/* Copyright 2020 (c) Adam McKenney - See LICENSE for details */
+/* Copyright 2021 (c) Adam McKenney - See LICENSE for details */
 /* A way slimmer version of cat without the GNU bloat features that I have never used nor needed */
-#include <stdio.h>   //fgetc, putchar, FILE, fopen, perror, fclose, puts, fprintf
+#include <stdio.h> //fprintf, perror
+#include <stdlib.h> //exit
+#include <unistd.h> //read, write, close
+#include <fcntl.h> //open
 
-#define NAME "slimcat"   //Program name, can be changed
+#define NAME "slimcat"   //Program name, can be changed so a user can keep their bloated version of cat
 #define HELP "Usage: " NAME " [-hu] [file...]\nWe concatenate files(s) to standard output with less than 50 lines of code.\n\nWith no file, or when file is -, read standard input.\nExamples:\n  " NAME " -h     Displays the help\n  " NAME " -u     Tells the OS that we dont want a buffer (warning may be a lot slower with a large file).\n  " NAME " x - y  Output x's contents, then standard input, then y's contents.\n  " NAME "        Copy standard input to standard output."
+#define BUFF_SIZE 10000 //a larger buffer trades memory for speed
 
-static char no_buf = 0; //-u option
-
-void throw_error(const char* extra_msg){
+void throw_error(char* extra_msg, int exit_code){
 /* function to writes the program name, optionally extra info, then the error to stderr */
 	if(extra_msg != NULL) fprintf(stderr, "%s: %s: ", NAME, extra_msg);
 	else fprintf(stderr, "%s: ", NAME);
 	perror("");
+	if(exit_code) exit(exit_code); //allows non-fatal errors to keep going
 }
-void cat(FILE *fp){
-/* loops through the file and puts the data one byte at a time into stdout until fread() returns 0 */
-	char p = 0;
-	if(no_buf) if(setvbuf(fp, &p, _IONBF, 1)) throw_error(NULL); //tell the OS we dont want a buffer
-	do 
-		if(!fread(&p, 1, 1, fp) || !fwrite(&p, 1, 1, stdout)) break; //if we were unable to read or write, we are done. Size must be 1 for binary files
-	while(1);
+void cat(int fd, char no_buf){
+/* reads from the file descriptor into buf, until zero bytes are read  */
+	char buf[BUFF_SIZE];
+	size_t r = 0, size = BUFF_SIZE;
+	if(no_buf) size = sizeof(char);
+	while((r=read(fd, buf, size)) > 0)
+		if(write(1, buf, r) != r) throw_error(NULL, 3); //if writing stops for some reason
+	if(r == -1) throw_error(NULL, 1); //if read(2) throws an error
 }
-int get_file(const char* file_name){
+int get_file(char* file_name, char no_buf){
 /* tries to open the user's file, then calls cat() with its file pointer */
-	FILE *fp = NULL;
-	if(file_name[0] == '-' && file_name[1] == '\0') fp = stdin; //if the user did 'cat -' or 'cat foo - bar'
-	else fp = fopen(file_name, "r");
-
-	if(fp == NULL){ throw_error(file_name); return 1; }
-
-	cat(fp);
-	fclose(fp);
+	int fd = -1;
+	fd = open(file_name, O_RDONLY);
+	if(fd == -1) throw_error(file_name, 1);
+	cat(fd, no_buf);
+	close(fd);
 	return 0;
 }
 int main(int argc, char *argv[]){
-/* takes the args -h for help and -u for unbuffered output */
-	size_t i;
+	size_t i = 0;
+	char no_buf = 0; //-u option
 	for(i=1; i < argc; i++){ //step through all the vars
 		if(argv[i][0] == '-' && argv[i][1] != '\0'){ //if its a command line arg
 			if(argv[i][1] == 'h') { puts(HELP); return 0; }
 			else if(argv[i][1] == 'u') no_buf = 1; //required by POSIX, turns off buffered output
 			else { fprintf(stderr, "%s: unknown command line arg '%s'\n", NAME, argv[i]); return 2;}
 		} else break;
 	}
-	if(argv[i] == NULL) cat(stdin); //if no args
-	else for( ; i < argc; i++) get_file(argv[i]); //step through each arg as if it's a file
+	if(argv[i] == NULL) cat(STDIN_FILENO, no_buf); //if no args
+	else for( ; i < argc; i++) get_file(argv[i], no_buf); //step through each arg as if it's a file
 	return 0;
 }
+