C programming- read from text file - c

Question

it's about reading from a text file.
I have 3 command line arguments:
name of text file
delay time
how many line(s) want to read.
I want to read that text file by user specified line numbers till text file ends.
For example, the first time I read 5 lines and then the program asks how many line(s) do you want to read?. I would enter 7 it reads lines 5 to 12.
This would repeat until the end of the file.
#include <stdlib.h>
#include <stdio.h>
#include<time.h>
#include <string.h>
void delay(unsigned int mseconds)
{
clock_t goal = mseconds + clock();
while (goal > clock());
}
int countlines(const char *filename) {
FILE *fp = fopen(filename, "r");
int ch, last = '\n';
int lines = 0;
if (fp != NULL) {
while ((ch = fgetc(fp)) != EOF) {
if (ch == '\n')
lines++;
last = ch;
}
fclose(fp);
if (last != '\n')
lines++;
}
return lines;
}
int main(int argc, char *arg[])
{
FILE *ptDosya;
char ch;
ch = arg[1][0];
int s2;
int satir = 0;
int spaceCounter=0;
int lineCount, x = 0;
lineCount = atoi(arg[3]);
s2 = atoi(arg[2]);
printf("dosya %d satir icerir.\n", countlines(arg[1]));
ptDosya = fopen(arg[1], "r");
if (ptDosya != NULL)
{
while (ch != EOF&& x < lineCount)
{
ch = getc(ptDosya);
printf("%c", ch);
if (ch == '\n')
{
delay(s2);
x++;
}
}
while (x < countlines(arg[1]))
{
printf("satir sayisi giriniz:");
scanf("%d", &lineCount);
// i don't know what should i do in this loop..
x=x+lineCount;
}
}
else {
printf("dosya bulunamadi");
}
printf("\n\nend of file!\n");
fclose(ptDosya);
return 0;
system("PAUSE");
}

Answer 1

Your delay function uses a busy loop. This is unnecessarily expensive in terms of computing power. It would be very unwelcome to do this on a battery operated device. Furthermore, clock() does not necessarily return a number of milliseconds. The unit used by the clock() function can be determined using the CLOCKS_PER_SEC macro. Unfortunately, there is no portable way to specify a delay expressed in milliseconds, POSIX conformant systems have usleep() and nanosleep().
Your line counting function is incorrect: you count 1 line too many, unless the file ends without a trailing linefeed.
Here is an improved version:
int countlines(const char *filename) {
FILE *fp = fopen(filename, "r");
int ch, last = '\n';
int lines = 0;
if (fp != NULL) {
while ((ch = fgetc(fp)) != EOF) {
if (ch == '\n')
lines++;
last = ch;
}
fclose(fp);
if (last != '\n')
lines++;
}
return lines;
}
There are issues in the main() function too:
You so not verify that enough arguments are passed on the command line.
You do not check for EOF in the main reading loop.
You do not repeat the process in a loop until end of file, nor do you even ask the question how many line(s) do you want to read? after reading the specified number of lines...

Answer 2

First, if the file cannot be found, the countlines method returns zero. You should use that value to write the error message, and skip the rest of the code.
Second, in the next loop, you use
if (ch != '\n') {
printf("%c", ch);
} else {
printf("\n");
delay(s2);
x++;
}
Why the two printf statements? They will print the same thing.
Perhaps something like this:
ch = getc(ptDosya);
/* exit the loop here if you hit EOF */
printf("%c", ch); /* Why not putc() or putchar() ? */
if (ch == '\n') {
x++;
if ( x == lineCount ) {
x = 0;
lineCount = requestNumberOfLinesToRead();
} else {
sleep(s2); /* instead of delay(). Remember to #include unistd.h */
}
}