File read

[compnub1]

Hi there,

I am having some problems prompting the user to enter a command in.

for example i want the command"print" to be recongised multiple time.

Its supposed to behave like this: Enter command > print

and then it prints out the contents of the file.

However when my program does this: Enter Command > print

print

and then it prints

i have to type print in 2 times for it to work. I been trying to figure what is the error but i cant see it.

  char input[100];
   
   fp = fopen(argv[1],"r");

   while(fopen(argv[1],"r")){

        printf("Enter command > ");

        fgets(input,100,stdin);

        if(strcmp(fgets(input,100,stdin),"print\n") == 0){
        //i have another while loop with fgets to read stuff in file

       }else if(strcmp(fgets(input,100,stdin),"quit\n") == 0)
         
        fclose(fp);        //closes program   

      }

}
     
 reutrn 0;

}

[zalezog]

fgets(input,100,stdin);

        if(strcmp(fgets(input,100,stdin),"print\n") == 0)

Used fgets(..) twice, i hope this is pseudo-code.

[compnub1]

Ok i got rid of the multiple fgets and it works but y does the command print not work after the first time??
Also when i enter the command quit the program wont close itself?/ why is that?

   char input[100];
   
   fp = fopen(argv[1],"r");

   while(fopen(argv[1],"r")){

        printf("Enter command > ");
       
        if(strcmp(fgets(input,100,stdin),"print\n") == 0)

       //i have loop to read stuff in from a file

       }else if(strcmp(fgets(input,100,stdin),"quit\n") == 0){

        fclose(fp); ///supposed to close the file
  
       }

  }

return 0;

}

[Salem]

> while(fopen(argv[1],"r"))
You keep re-opening the file.

> if(strcmp(fgets(input,100,stdin),"print\n") == 0)
Separate them into separate steps.
fgets() can return NULL, which would hose your strcmp

[compnub1]

I have to keep the file open so that it can keep printing "Enter command >". Also i dont get what you mean by fgets hosing the strcmp. The print command only works once and the exit command doesnt work at all.I went through it logically and dont know why it is wrong.

[Salem]

The file is open until you close it.

> Also i dont get what you mean by fgets hosing the strcmp
If fgets() returns NULL, which it does at end of file, you have
strcmp( NULL, "print\n")

As soon as strcmp() dereferences NULL, it's bye bye program in a segmentation fault.

[compnub1]

i got to keep printing Enter command > when the user has not finish issuing commands and then the program ends itself through the command quit. So how do i do this and at the same time compare it to a command i enter like "print". Also my quit command wont work. Any ideas why?
I also corrected it to compare to NULL.

char input[100];
   
   fp = fopen(argv[1],"r");

   while(fopen(argv[1],"r")){

        printf("Enter command > ");
       
        if(strcmp(fgets(input,100,stdin),"print\n") == 0 && !NULL){

           //i have loop to read in the stuff from file

     }else if(strcmp(fgets(input,100,stdin),"quit\n") == 0){

        fclose(fp); //why does quit command not work
  
       }

}

return 0;

}

[Salem]

This is what I mean by comparing with NULL

while ( fgets ( input, sizeof input, fp ) != NULL ) { /* This compares to NULL */
    if ( strcmp( input, "print\n") == 0 ) {
        FILE *fp = fopen("argv[1],"r");
        // read from fp here
        fclose( fp );
    } else
    if ( strcmp( input, "quit\n" ) == 0 ) {
        break;
    }
}

It doesn't print a prompt, but that's an exercise for you.