将命令行参数和文本文件传递给程序

Question

I have a Read and Reverse Coding assignment where I need to pass a Textfile and a character ( -L , or -W ), depending on whether the operator wants the textfile returned in reverse by lines or by words. (I should also note that the assignment requires that nothing is asked of the user during the code. It must be decided which variation is wanted in the command line.)

I don't need help with the code to reverse the lines or words, but do need help with understanding how to take in character and the textfile, then use them in the code. I've tried using the parameters (int argc, char *argv[]) on the main , but anytime I try to pass in just the -L the terminal either says Command not found or clang: error: argument to '-L' is missing (expected 1 value)

Also, when my teacher passes a textfile to a program he often uses a > . Can someone explain how to use this?

Ex. program.c > hello.txt

Then he would end up using that .txt in the program.

Answer 1

Consider this:

program -L < data.txt

or

program -W < data.txt

or

cat data.txt | program -L

The "-L" or "-W" will be in argv[1] .

Good luck!

Answer 2

The idea of Passing a Command Line Arguement is the following

Argc : argument counter amount of "strings"(arguments) passed for execution. Its always 1 or greater as the calling of the function is an argument.

Argv : argument vectors(pointers), is a pointer to each of the arguments received by the command line

Example of program call:

./myprogram -w

argc=2

argv will have two pointers to strings(char):

argv[0]= "./myprograms"

argv[1]= "-w"

Now with your problem

When excecuting a program via command line you have a lot of options amongst these:

1) One of these is to give the program input of a file(the file will be passed character by character to the standard input ending with an EOF or -1 -not an ascii character-) These can be done by the follow way

./program.c < hello.txt

2)Redirect the output of the program to a file

./program.c > hello.txt

What you are looking to do is input a file while passing an argument this can be done the following way

./program.c < hello.txt -L

IMPORTANT : "< hello.txt" will NOT count as an argument so for this case the case the argc and argv will be the follow

argc=2

argv[0]="./program.c"

argv[1]="-L"

Hopes this helps comment if you need anymore help or something isn't clear. Good luck with your course!!!