CODEWITHSUNDEEP
cshellosx-mavericksargc
tf3
tf3

Reputation: 467

argc giving erroneous value in C program

I want to enter some command line arguments at run time. Like

./program abc def ghi

argc would be 4 in this case. No problem in this. But if I do

./program abc def *

or even

./program * abc def

the variable argc gives me a value far larger than 4.

On printing the entire argv array (leaving aside the 0th argument; ./program) as strings, I am given a list where the first two elements are abc and def and the others are all file names of the files contained in the working directory.

I am trying to learn C from K&R. I was trying to make an RPN calculator where we can give expressions like ./program 2 4 *.

What is the reason for this? Or am I wrong somewhere?

Upvotes: 3

Views: 484

Answers (4)

Ryan
Ryan

Reputation: 14649

If you're using bash, start the shell with the -f switch to turn off expansion of things like *

bash -f

Upvotes: 2

Dmitry Grigoryev
Dmitry Grigoryev

Reputation: 3203

You can prevent * from expanding into file names by putting it into single quotes, i.e.

./program 2 4 '*'

This way your program will receive 3 input arguments with values "2", "4" and "*" in terms of C strings.

Upvotes: 0

Shahbaz
Shahbaz

Reputation: 47553

Shells have a feature called globbing, where they expand certain patterns, such as * to the matching files. If in the current directory you have the following:

file1 file2 somethingelse dir1

then calling:

any_program *

will be equivalent to:

any_program file1 file2 somethingelse dir1

Or if you do:

any_program fi*

it will be equivalent to:

any_program file1 file2

This is a feature of the shell. Your C program is well-behaved.

Since shells are different, let's assume you are using bash. To prevent bash from performing expansions, you should quote the argument. For example:

any_program "fi*"

will actually pass fi* to your program, without expanding it to file1 file2.

Upvotes: 10

Evil Dog Pie
Evil Dog Pie

Reputation: 2320

The commandline interpretter processes the * character as a wildcard before passing the arguments to your program, just the same as it does if you type DIR *.

The simple solution is to devise a meaningful parameter that does not get interpretted.

Upvotes: 3

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