Lecture on Reading Files in C

Common Programming Task

• One of the most common programming tasks in STEM fields is opening a file, reading data, and analyzing it.
• This lecture focuses on learning how to open a file and read data in C.

Setting Up

• Use the Command Prompt:
  • Search for CMD and open Command Prompt.
  • Navigate to the desktop and relevant directory using cd commands.
• Create a batch file for the program: average uncore ofor file.

Creating a Data File

• You can create a data file using Notepad++ or directly from Command Prompt:
  • Command: echo. > data file.txt creates an empty file named data file.txt.

Preparing the C Program

• Open the newly created project folder and files using Notepad++.
• Use a template from a previous average scanf program:
  • Copy (Ctrl+A, Ctrl+C) the entire program and paste (Ctrl+A, Ctrl+V) it as a starting point.

File Handling in C

• File Pointer:
  • Declare a file pointer: FILE *FP;
  • FILE is a special type of variable, and C is case-sensitive.
  • FP stands for File Pointer.
• Opening a File:
  • Use fopen command: FP = fopen("data file.txt", "r");
  • First argument is the file name, second is the mode ('r' for read).
  • C does not error check file operations, so manual checks are necessary.
• Reading from a File:
  • Use fscanf instead of scanf:
    • First argument is FP, followed by format string and variables.
  • Include a printf statement for diagnostics to confirm data is loaded correctly.

Running the Program

• Save changes (Ctrl+S).
• Enter 10 random numbers in data file.txt.
• Compile and run the program to verify data is read correctly and average is calculated.
• Manually check the average calculation to ensure accuracy.

File Closure

• Use fclose(FP); to close the file after operations are complete.
• Closing files is a best practice to prevent potential issues, although C will not break immediately if you forget to close files.
• Remember to close files after reading/writing as a good housekeeping measure.