#include <stdio.h>	// for "fprintf" and "fgetc"
#include <stdlib.h>	// for "exit"

	// function prototypes 
void fatal (int retv, char *message);
int streamline (FILE *IN);

char *buffer;		// global buffer

int main (int argc, char *argv[]) {	// argv[1] will be the filename to read
	FILE *fstRO, *fstOUT;		// argv[2] will be the filename to write
	int retv, ln=1; // ln is for line number
	
	if (argc<2) fatal(-1,"Two filenames required.");	// check for them
		
		// open the files
	if ((fstRO=fopen(argv[1],"ro"))==NULL) fatal(-2,"Can't read from file #1.");
	if ((fstOUT=fopen(argv[2],"w"))==NULL) fatal(-2,"Can't write out to file #2.");

	while ((retv=streamline(fstRO))>0) {		// read from file
		fprintf(fstOUT, "%d. %s\n",ln,buffer); 	// write to file
		ln++; 	// increment
		free(buffer);	// very important since buffer had memory allocated in streamline()
	}
	
	switch (retv) {		// finished reading file
		case -2: fatal(-3,"Memory allocation failure!"); 	// in case streamline() fails
		case -1: fprintf(fstOUT, "%d. %s\n",ln,buffer);		// the "special case"
			break;
		case 0:	break;
		default: break;
	}
	free(buffer);	// less important since the program is now over	
		// close the files
	fclose(fstRO);
	fclose(fstOUT);
	return 0;		// THE END
}

void fatal (int retv, char *message) {
	puts(message);
	exit (retv);
}

int streamline (FILE *IN) {	// returns a string length that INCLUDES the line terminator or 0 for last line
	int chr, i=0;		// i is for iteration counter
	buffer=malloc(1);	// begin allocating memory for the line buffer
	while ((chr=fgetc(IN))!=EOF) {
		if (buffer==NULL) return -2;		// in case memory allocation fails
		if (chr=='\n') {	// reached end of line
			buffer[i]='\0';	// so terminate it
			return i+1;
		}
		buffer[i]=chr;		// copy character into buffer
		buffer=realloc(buffer,++i+1);	// more memory for next iteration
	}	// End-Of-File reached
	if (buffer==NULL) return -1;	// last check
	if (i>1) {
		buffer[i]='\0';		// terminate last line if it exists with no newline
		return -1;		// (a normative "special case")
	}
	return 0;		// and return 0 to indicate we're finished
}