Thread: Manipulating a read-in file in C

Forgive my ignorance Tater, but are you referring to replacing part of my existing code, fopen() with fgets()? Or are you referring to the next step in the process below what I already have. I am confused. Thanks

EDIT: fopen() and fgets() are 2 totally differnet things, nevermind. I'll figure it out eventually..

You need to rethink your approach to the problem...
Look at your file... it is line based... that is the data on each line is a complete data set of it's own. i.e. "Mike 90,80,75,100,100" contains all the information you need to process that line. Therefore you do not want to read the file in character by character as your first code would. It may echo the file to the screen very nicely but it doesn't give you meaningful access to the information in the file... for that you need some kind of structured input routine.

As it turns out C libraries provide several ways of doing this... you can use fscanf() to read in a complete line at a time, so long as each line has the same number of parameters on it... (A name and 5 numbers per your example). If some lines have more or less than 5 numbers you will need to use a slightly different strategy in which case you can use fgets() to read a line from the file into a string variable and then extract the values from there using other library functions such as strtok(), atoi(), sscanf() etc.

fopen() is for opening files... fgets() is one of many ways you can read a file's contents... so yes they're different things.

Look these various functions up in your C libary documentation.

Here's a tutorial on files that may help you... C Tutorial - Chapter 10

Hi again,

I couldn't figure out how to do it your way Tater, so I decided to try to read-in the file by character rather than line. I am getting 1 error and 14 warnings with this, and I am not sure how to proceed from here. I have commented the error towards the bottom of the code. The 14 warnings are mostly conversion warnings (int to float) (double to float).....Here is the code, I hope I didn't make this more complicated than it needs to be. Any ideas?.....


*EDIT* I figured out the Error part, but that still leaves me with the 14 warnings. I should probably clean this up....

Code:

#include <stdio.h>


int main(void)
{
	int ch;
	int track=1;
	FILE * fp;
	char name[999];
	char quiz1[3];
	char quiz2[3];
	char quiz3[3];
	char quiz4[3];
	char midterm[3];
	char finalproject[3];
	float q1;
	float q2;
	float q3;
	float q4;
	float mid;
	float final;
	float total_grade=0;
	int index=0;
	fp = fopen("C:\\Documents and Settings\\xxxx\\Desktop\\Final_Input.txt", "r");
	ch = getc (fp);
	name[index]=ch;
	index++;
	while (ch != EOF)
	{
		//putchar(ch);
		ch= getc(fp);
		if(track==1)
		{
			if(ch==',')
			{
				name[index]='\0';
				track++;
				index=0;
			}
		else
			{
				name[index]=ch;
				index++;
			}
		}
		else if(track==2)
		{
			if(ch==',')
			{
				quiz1[index]='\0';
				q1=atoi(quiz1);
				total_grade=total_grade+q1*.10;
				track++;
				index=0;
			}
			else
			{
				quiz1[index]=ch;
				index++;
			}
		}
		else if(track==3)
		{
			if(ch==',')
			{
				quiz2[index]='\0';
				q2=atoi(quiz2);
				total_grade=total_grade+q2*.10;
				track++;
				index=0;
			}
			else
			{
				quiz2[index]=ch;
				index++;
			}
		}
		else if(track==4)
		{
			if(ch==',')
			{
				quiz3[index]='\0';
				q3=atoi(quiz3);
				total_grade=total_grade+q3*.10;
				track++;
				index=0;
			}
			else
			{
				quiz3[index]=ch;
				index++;
			}
		}
		else if(track==5)
		{
			if(ch==',')
			{
				quiz4[index]='\0';
				q4=atoi(quiz4);
				total_grade=total_grade+q4*.10;
				track++;
				index=0;
			}
			else
			{
				quiz4[index]=ch;
				index++;
			}
		}
		else if(track==6)
		{
			if(ch==',')
			{
				midterm[index]='\0';
				mid=atoi(midterm);
				total_grade=total_grade+mid*.25;
				track++;
				index=0;
			}
			else
			{
				midterm[index]=ch;
				index++;
			}
		}
		else if(track==7)
		{
			if(ch==',')
			{
				finalproject[index]='\0';
				final=atoi(finalproject);
				total_grade=total_grade+final*.35;
				track++;
				index=0;
			}
			else
			{
				final[index]=ch;  //subscript requires array or pointer type
				index++;
			}
		}
	}
	//printf("%.2f",total_grade);
}

Ok... using this as your example,

Mike 90,80,75,100,100

Look at this line... what do you see?
I see a string and 5 integers, separated by commas.
So what we need is some kind of formatted read utility that can fetch this from a file for us...
That would be fscanf() ... (Yes, look it up!)

With me so far?

Now... we need to
1) open your input file,
2) open your output file,
3) read one line from the input file with scanf()
4) Calculate the average
5) Write it to the output file
6) check for end of input file
7) if not end of file loop back to #3
8) close the input file
9) close the output file


Write that and lets see how you make out...
Seriously... we're talking about less than 30 lines of code here....
how hard can it be?

Ok, I think I am getting somewhat closer and getting the general concept of fscanf(). Here is my latest attempt, I am getting 0 errors but 5 warnings. Warnings such as firstname isn't intialized, last name isn't intialized and "incompatible types - from 'FILE *' to 'const char *'. Also, nothing prints to the screen. The console opens but I get nothing...

Am I close? Thanks again...


*EDIT* I realized I needed to turn firstname, lastname into arrays. Not a single char. So now it prints, but it is printing weird symbols, not what is on the file...

Code:

#include <stdio.h>
#include <string.h>

int main()
{
  
  char firstname [50];
  char lastname [50];
  float q1,q2,q3,q4,mid,final;
  FILE *fp;
  char my_filename_input[] = "C:\\Documents and Settings\\xxxx\\Desktop\\Final_Input.txt";
  fp=fopen (my_filename_input, "r");
  fscanf (fp, "%s, %s, %f, %f, %f, %f, %f\n",firstname,lastname,&q1, &q2, &q3,&q4,&mid,&final);
  printf (fp, "%s %s %f %f %f %f %f", firstname,lastname,q1, q2, q3,q4,mid,final);
  
}

Can you give me a sample of the exact file... 10 or 20 lines?

Also, are you sure the grade scores need to be floats... if the scoring runs the typical 0 - 100 ints would work better.

Your scanf is very close and your printf almost works...

Code:

  fscanf (fp, "%s %s %f,%f,%f,%f,%f",firstname,lastname,&q1, &q2, &q3,&q4,&mid,&final);
  printf ("%s %s %f %f %f %f %f", firstname,lastname,q1, q2, q3,q4,mid,final);

Note... this is one case where spacing does matter...