system(); not allowing me to pass in variables

Question

I'm trying to make something that compiles and runs .c files in one command. But I'm having a problem. I got the filename through the get_string(); under the_ cs50.h_ library.

And now I'm to give the system() function this command make {filename} by doing this

system("make %s", filename")

But it just gives this error back:

mac.c:18:23: error: too many arguments to function call, expected single argument '__command', have 2 arguments
    system("make %s", filename);
    ~~~~~~            ^~~~~~~~

I understand that It means that the system() function has too many arguments but I don't know any other way to add in the filename after make.

Here is a copy of the code I am using if you need to look at it more. Thanks! Click Here to go to the github page If you find a fix, either comment it or you can do a pull request at the github!

I realized that, that's why I need a alternative way to combine them — okistuff, May 07 '20 at 20:04

score 2 · Answer 1 · answered May 07 '20 at 20:05

2

system() only takes a single parameter. You need to build up the string beforehand, and then pass it already built.

For that, you probably are looking for a function like sprintf().

answered May 07 '20 at 20:05

Acorn

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By any chance could I have an example on how to do it. Thanks! – okistuff May 07 '20 at 20:07
@TECHSCHOOL200000 The best you can do is search for questions about `sprintf` like [this one perhaps](https://stackoverflow.com/questions/2674312/how-to-append-strings-using-sprintf). – Acorn May 07 '20 at 22:31

Roberto Caboni · Accepted Answer · 2020-05-07T20:32:15.377

2

That compilation error is raised because system() expects only one string argument.

If you need to make the command dependent to a parameter, first build it with sprintf:

char command[256];

sprintf(command, "make %250s", filename);
system (command);

The %250s format is to avoid that, in the unlikely case that filename is longer than 250 characters, we go out of bounds of command array.

A safer function allowing to limit the total length is snprintf:

snprintf(command, 255, "make %s", filename);

edited May 07 '20 at 20:32

answered May 07 '20 at 20:08

Roberto Caboni

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If `filename` is over 250 characters, this will end badly. – Joseph Sible-Reinstate Monica May 07 '20 at 20:17
1

It works! Just little notice. instead of `sprinf( command, "{command}", filename" )` just do `sprinf( command, "{command}", filename )` – okistuff May 07 '20 at 20:19
@JosephSible-ReinstateMonica you know, I was writing my `snprintf` solution or the `%250s` one. But since I didn't want to explain that part I thought that the simple sprintf was enough. Well: SOguys doesn't forgive! I'll edit it. – Roberto Caboni May 07 '20 at 20:23
@JosephSible-ReinstateMonica PS: on Windows MAX_PATH is 260... – Roberto Caboni May 07 '20 at 20:24
@TECHSCHOOL200000 you are right. I'm sorry fo the rejected edit. The system rejected it because I was editing the answer as well. – Roberto Caboni May 07 '20 at 20:35

system(); not allowing me to pass in variables

2 Answers2