Thread: Reading in any File

I'm brand new to c programming, and have an assignment that requires me to call on functions and manipulate data files etc.
I decided to practice just to try and get the hang of reading in a single file and displaying at least a part of that file on the screen. The problem is when the program prompts me to type in the filename it is not able to find it.
I have a hinting suspicion that it has something to do with how I've gone about trying to allow the user to input the filename.
Any advice or help would be greatly appreciated as I am extremely new to all of this

Code:

#include <stdio.h>
#include <stdlib.h>
    
int main()
{
    FILE *filep;
    char filename;
    float x, y;
     
     
     printf("Please enter name of file to be arranged and stored\n");
     scanf("%c",&filename);
     filep = fopen("&filename","r");
    
    if(filep != NULL)
     {
        fscanf(filep, "%f %f",&x, &y);
        printf("The first value is %f\nThe second value is %f",x,y);
        fclose(filep);
     }
     else 
     {
         printf("The file was unable to be opened, please try again");
     }
    return (0);
}

Thanks for your time and effort and sorry if the code is completely wrong :/

cheers daeze

A hinting suspicion?? XD

Yes never do this without an array of characters. Cut him some slack he's new XD

Okay thanks for your help I have fixed the faults according to what you suggested and the is what it comes up with

Code:

Please enter name of file to be arranged and stored
sp500.dat
Program received signal:  “SIGABRT”.sharedlibrary 
apply-load-rules all(gdb) 

Which is better than failing to open anything but still not what I was hoping for. I researched fgets and not quite sure what it does or how to use it, but If you believe it is a better approach I will give it a go here is the revised code:

Code:

#include <stdio.h>
#include <stdlib.h>
	
int main()
{
	FILE *filep;
	char filename[8];
	float x, y;
	 
	 
	 printf("Please enter name of file to be arranged and stored\n");
	 scanf("%s",filename);
	 filep = fopen(filename,"r");
	
	if(filep != NULL)
	 {
		fscanf(filep, "%f %f",&x, &y);
		printf("The first value is %f\nThe second value is %f",x,y);
		fclose(filep);
	 }
	 else 
	 {
		 printf("The file was unable to be opened, please try again");
	 }
	return (0);
}

Also, I was wondering how to make it so 'any' file could be opened no matter how many characters in the name? is that what the 'fgets' function does? or should i create a variable for the character array?Again thanks heaps for your time and sorry for my noobishness :/cheers daeze

I'm still a noobie to C as well. Correct me on anything if I'm wrong guys! Only been doing this since January. My past 4 or so assignments have been dealing with files and plenty more.I'm not sure of another way than dynamic memory allocation to get a different size for the filename. If you're not worried about that just put a reasonable size in the brackets for filename.

I researched fgets and not quite sure what it does or how to use it

fgets - C++ Reference fgets has 3 parts and looks like this

Code:

fgets(string, number_of_characters_read, pointer_to_file)

it uses the pointer to the file to store that line into your character of strings (which in the code I put is "buffer"). The middle part is the number of characters it reads in that string (which is why I always just put sizeof(buffer)).Here's what I came up with for your code. Worked on my computer. But like I said, I'm still new. I'd take any advice from the people above me first!

Code:

#include <stdio.h>#include <stdlib.h>
     
int main()
{
    FILE *filep;
    char filename[50];  //Defines up to how many characters in the filename
    char buffer[50];    //Stores the data in each line in buffer
    float x, y;
      
     printf("Please enter name of file to be arranged and stored\n");
     scanf("%s",&filename);
     
     //Opens the file
    if ( (filep = fopen(filename, "r")) == NULL )
    {
     printf("Couldn't open file\n");
     exit(1); 
    } 
     //Reads the file line by line
    while( fgets(buffer, sizeof(buffer), filep))
     {
        sscanf(buffer,"%f %f", &x, &y);
        printf("The first value is %f\nThe second value is %f\n",x,y);
        getchar();
     }
    fclose(filep); 
return (0);
}

Originally Posted by ledow

Code:

sp500.dat
char filename[8];

Spot the deliberate mistake. But I'm sure it's not the only one.

Obviously I'm very new because i thought that if I wanted 9 characters I needed to include '0' so a character array of [8] would give me the 9 characters i need. My friend from class however pointed out that this is not the case so I have since fixed it.

Thanks very much for your help mgracecar! Theres some language in your code that I am studying to get a grip of what you did, so it was very informative I too tried it and it originally didnt work. After hours of frustration i decided to open a new file in xcode and try again for scratch. I also changed the path of the executable code and repasted your code in. It worked a treat and since has worked for all my other code, so I think it was just a permission in the previous file that was causing all the trouble!

My job now is to put the data from the file into two arrays name x[] and y[], Ill keep you posted on how i go and will probably need some more friendly advice after I've had a good crack at it thanks to all who have offered your time and support. Much appreciated

cheers 'A very relieved' daeze

Originally Posted by ledow

In general, filenames are less than 256 characters because a lot of operating systems can't handle that amount of characters in a filename or command line anyway.

Thats very helpful ledow thanks. I will use that tip from now on. I was just apprehensive at first as I thought the file may not open if i assign too much space in the array, but obviously it doesnt so I will use the 256 buffer size as a general rule from now on

cheers daeze