C function that counts lines in file

Question

When I try to run my program, I get the wrong number of lines printed.

LINES: 0

This is the output although I have five lines in my .txt file

Here is my program:

#include<stdio.h>
#include<stdlib.h>

int countlines(char *filename);

void main(int argc, char *argv[])
{
  printf("LINES: %d\n",countlines(argv[1]));         
}


int countlines(char *filename)
{
  // count the number of lines in the file called filename                                    
  FILE *fp = fopen(filename,"r");
  int ch=0;
  int lines=0;

  if (fp == NULL);
  return 0;

  lines++;
  while ((ch = fgetc(fp)) != EOF)
    {
      if (ch == '\n')
    lines++;
    }
  fclose(fp);
  return lines;
}

I am sure it is a simple mistake but I am new to programming. Any help would be greatly appreciated.

Answer 1

while(!feof(fp))
{
  ch = fgetc(fp);
  if(ch == '\n')
  {
    lines++;
  }
}

But please note: Why is “while ( !feof (file) )” always wrong?.

Answer 2

The accepted answer takes 34 (!) seconds to count lines in a 1.3 Gb CSV file on my Core i9 CPU and SSD drive. Please, don't use fgetc to read large files. This is prohibitively slow. The following snippet does the job in 300 ms:

#include <stdio.h>

#define BUF_SIZE 65536

int count_lines(FILE* file)
{
    char buf[BUF_SIZE];
    int counter = 0;
    for(;;)
    {
        size_t res = fread(buf, 1, BUF_SIZE, file);
        if (ferror(file))
            return -1;

        int i;
        for(i = 0; i < res; i++)
            if (buf[i] == '\n')
                counter++;

        if (feof(file))
            break;
    }

    return counter;
}

Answer 3

You declare

int countlines(char *filename)

to take a char * argument.

You call it like this

countlines(fp)

passing in a FILE *.

That is why you get that compile error.

You probably should change that second line to

countlines("Test.txt")

since you open the file in countlines

Your current code is attempting to open the file in two different places.

Answer 4

You have a ; at the end of the if. Change:

  if (fp == NULL);
  return 0;

to

  if (fp == NULL) 
    return 0;

Answer 5

You're opening a file, then passing the file pointer to a function that only wants a file name to open the file itself. You can simplify your call to;

void main(void)
{
  printf("LINES: %d\n",countlines("Test.txt"));
}

EDIT: You're changing the question around so it's very hard to answer; at first you got your change to main() wrong, you forgot that the first parameter is argc, so it crashed. Now you have the problem of;

if (fp == NULL);   // <-- note the extra semicolon that is the only thing 
                   //     that runs conditionally on the if 
  return 0;        // Always runs and returns 0

which will always return 0. Remove that extra semicolon, and you should get a reasonable count.

Answer 6

Here is my function

char *fileName = "input-1.txt";
countOfLinesFromFile(fileName);

void countOfLinesFromFile(char *filename){
FILE* myfile = fopen(filename, "r");
int ch, number_of_lines = 0;
do
{
    ch = fgetc(myfile);
    if(ch == '\n')
        number_of_lines++;
}
while (ch != EOF);
if(ch != '\n' && number_of_lines != 0)
    number_of_lines++;
fclose(myfile);
printf("number of lines in  %s   = %d",filename, number_of_lines);

}

Answer 7

I don't see anything immediately obvious as to what would cause a segmentation fault. My only suspicion is that your code expects to get a filename as a parameter when you run it, but if you don't pass it, it will attempt to reference one, anyway.

Accessing argv[1] when it doesn't exist would cause a segmentation fault. It's generally good practice to check the number of arguments before trying to reference them. You can do this by using the following function prototype for main(), and checking that argc is greater than 1 (simply, it will indicate the number entries in argv).

int main(int argc, char** argv)

The best way to figure out what causes a segfault in general is to use a debugger. If you're in Visual Studio, put a breakpoint at the top of your main function and then choose Run with debugging instead of "Run without debugging" when you start the program. It will stop execution at the top, and let you step line-by-line until you see a problem.

If you're in Linux, you can just grab the core file (it will have "core" in the name) and load that with gdb (GNU Debugger). It can give you a stack dump which will point you straight to the line that caused the segmentation fault to occur.

EDIT: I see you changed your question and code. So this answer probably isn't useful anymore, but I'll leave it as it's good advice anyway, and see if I can address the modified question, shortly).

Answer 8

I feel @Lundin 's answer was almost correct but you need to add a (lines++) command outside the loop cause the last line is not counted that way as it does not contain a \n.

Answer 9

Here is complete implementation in C/C++

#include <stdio.h>

void lineCount(int argc,char **argv){

        if(argc < 2){
             fprintf(stderr,"File required");
             return;
        }
        FILE *fp = fopen(argv[1],"r");



        if(!fp){
            fprintf(stderr,"Error in opening file");
            return ;      
        }

        int count = 1; //if a file open ,be it empty, it has atleast a newline char
        char temp;

        while(fscanf(fp,"%c",&temp) != -1){
                if(temp == 10) count++;
        }

        fprintf(stdout,"File has %d lines\n",count);
   }

int main(int argc,char **argv){

        lineCount(argc,argv);
        return 0;
}
https://github.com/KotoJallow/Line-Count/blob/master/lineCount.c