error handling c programming tutorial

certainly! error handling in c programming is crucial for building robust applications. in c, error handling is typically done through return values, error codes, and sometimes with the use of `errno` and related functions. this tutorial will explain these concepts and provide examples.

error handling in c

1. return values
many c library functions indicate success or failure through their return values. for example, functions may return `0` for success and a negative value or `-1` for failure.

2. `errno`
the global variable `errno` is used by system calls and library functions in c to indicate what error occurred. it is set to zero at the beginning of a program and is updated when a function fails.

3. error codes
in c, specific error codes are defined in the `errno.h` header file. common error codes include:
- `einval`: invalid argument
- `enomem`: out of memory
- `eio`: input/output error
- `eperm`: operation not permitted

example: file handling with error handling

in this example, we will demonstrate error handling using file operations. we will attempt to open a file, read from it, and handle possible errors.

explanation of the code

1. **include necessary headers**:
- `stdio.h` for file operations.
- `stdlib.h` for general functions.
- `errno.h` for error numbers.
- `string.h` for the `strerror()` function.

2. **function `readfile`**:
- it takes a filename as an argument and attempts to open it for reading.
- if `fopen` fails, it returns `null`, and we print an error message using `strerror(errno)` to retrieve a human-readable error message based on the error code stored in `errno`.

3. **reading from the file**:
- we use `fgets` to read lines from the file. if an error occurs, we check it with `ferror()` and print an error message.

4. **closing the file**:
- we check the return value of `fclose()`. if it fails, we print another error message.

5. **in `main`**:
- we call the `readfile` function with a fil ...

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