Command Line Arguments in C

Command line arguments in C are a way to pass arguments to a program when it is invoked from the command line. Command line arguments are typically used to specify input files, output files, and other configuration options for the program.

In C, command line arguments are passed to the `main` function through its arguments. The `argc` parameter is an integer that specifies the number of command line arguments, and the `argv` parameter is an array of strings that contains the actual arguments.

The syntax for the `main` function with command line arguments is:

int main(int argc, char *argv[]) {
  // program code
}

Here, `argc` is the number of command line arguments, including the name of the program itself, and `argv` is an array of strings that contains the command line arguments as null-terminated strings.

For example, the following code reads a file name from the command line arguments and opens the file for reading:

#include 

int main(int argc, char *argv[]) {
  if (argc < 2) {
    printf("Usage: %s \n", argv[0]);
    return 1;
  }

  FILE *file = fopen(argv[1], "r");
  if (file == NULL) {
    printf("Error: cannot open file %s\n", argv[1]);
    return 1;
  }

  // read file contents

  fclose(file);
  return 0;
}

Here, the program checks whether at least one command line argument is provided (in addition to the program name), and prints an error message if not. If a file name is provided, the program attempts to open the file for reading, and prints an error message if it cannot be opened. The file contents can then be read and processed as needed.

It’s important to note that command line arguments are passed as strings, so any numeric or other non-string values must be converted to the appropriate data type before they can be used in the program. In addition, command line arguments are not guaranteed to be well-formed or valid, so it’s important to validate and sanitize the arguments before using them in the program.