Fopen Fails to read from Command line

Question

Fopen return NULL based on

now I have one file to read and I want to output on console but it throws an error as fp return NULL here a snippet

#include<stdio.h>

int main(char argc,char **argv)
{
      if(argc < 2)
      {
            printf("Usage:\t");
            printf("Hash File path");
      }

      printf("Hash File  : %s\n", argv[1]);
      FILE *fp = fopen("argv[1]","r");
      if(fp == NULL)
      {            
            fprintf(stderr,"Can't open %s\n", argv[1]);
      }
      else
      {
           char buff[100];
           while(!feof(fp))
           {
                if(fgets(buff,100,fp) == NULL) break;
                fputs(buff,stdout);
           }
            fclose(fp);
      }
      return 0;
}

whenever I pass file Path E:\design\test.txt from the command line it always shows error report "Can't open...." like this

so the confusion is

why Fopen Failed to read from Command line?

You are stating facts. Please add a specific question to your post. — Frederik.L, Sep 08 '18 at 05:29
Nisarg, there is still no question mark in your question, suggesting that you are not expecting any answer. The right answer at the moment is to say `ok`. New members *MUST* realize that the Q&A is to help future visitors with similar questions. During the process, you really need to think about how a visitor will ever get to your question, and nonetheless how likely the answers will be relevant. Failing to understand that is a bad experience for other members (waste of time), and for the poster (downvotes). What could really help your question is to have one, then improve the title. — Frederik.L, Sep 08 '18 at 05:52

Achal · Accepted Answer · 2018-09-08T05:45:44.223

There are few issues in code. Firstly, this

FILE *fp = fopen("argv[1]","r");

is wrong. First parameter of fopen() should be just argv[1] instead of "argv[1]". For e.g

FILE *fp = fopen(argv[1],"r");
if(fp == NULL) {            
     fprintf(stderr,"Can't open %s\n", argv[1]);
     return 0; /* this you forgot, if fopen fails,then no need to proceed further */
}

Also if argc<2 is true then just wrinting printf() is not enough, you have to ask user to give correct command line input & don't let user proceed further. It should be

if(argc < 2) {
      printf("Usage:\t");
      printf("Hash File path");
      return 0; /* return from here or use exit(0) */
 }

Secondly, Read here why feof() is wrong. You can use it like

while(fgets(buff,100,fp) != NULL) { /* no need to use break */
        fputs(buff,stdout); 
}

instead of

while(!feof(fp))
{
        if(fgets(buff,100,fp) == NULL) break;
        fputs(buff,stdout);
}

Fopen Fails to read from Command line

1 Answers1