CODEWITHSUNDEEP
c++windowscommand-line
Tod
Tod

Reputation: 8242

Why does using system("some.exe") in C++ method not work like the command line?

I am writing a program for Windows that eventually has to launch a different pre-existing .exe that sits on the same computer. It passes multiple parameters to this .exe file. I am reading the actual command and parameters and constructing the command but I also tried hard coding it with the same results. Here's the hard coded version (I picked this out of an older C program that uses the same.exe):

system("c://IQapture//dmon2_6_IHD -p2 c://IQapture//mon_table_101_Tx8.txt 11 0 0");

So in the original program inside int _cdecl main(int argc, char**argv) this use of system works. In my C++ program inside a C++ class method when I issue the command the correct program launches but it immediately puts up an error dialog stating that an error has occurred. I echo'd the system string used to launch the exe out to the console. Right after it fails, I copy and paste the same line that was echo'd and this time the exe runs without error. This is repeatable. In case it was timing related I tried adding a 10 second delay before issuing the system command but it didn't matter. Plus the original older program doesn't require a delay. This implies to me that the string is correct and the target program works. Somehow the system() invocation is different from a direct command line invocation. The program compiles and builds fine. I'm using Visual Studio 2010.

Does anyone have ideas on how to make the system() invocation work like the command line invocation?

Upvotes: 1

Views: 2479

Answers (3)

Loki Astari
Loki Astari

Reputation: 264381

You have your slashes backwards. Try:

system("c:/IQapture/dmon2_6_IHD -p2 c:/IQapture/mon_table_101_Tx8.txt 11 0 0");

You can use the backslash \ but because that is an escape sequence starter in a string (for C/C++) that is why you use two in a row. As the compiler will convert \\ into a single slahs in the string:

Thus:

system("c:\\IQapture\\dmon2_6_IHD -p2 c:\\IQapture\\mon_table_101_Tx8.txt 11 0 0");

// Is equivelent to the command line string:

> c:\IQapture\dmon2_6_IHD -p2 c:\IQapture\mon_table_101_Tx8.txt 11 0 0

But Windows has supported both types of slashes for longer than I can remember. So the following command line is equivalent.

> c:/IQapture/dmon2_6_IHD -p2 c:/IQapture/mon_table_101_Tx8.txt 11 0 0

Using '/' in a string (in C/C++) does not require escaping. So you just need to use it as is:

system("c:/IQapture/dmon2_6_IHD -p2 c:/IQapture/mon_table_101_Tx8.txt 11 0 0");

Upvotes: 1

paddy
paddy

Reputation: 63471

That really doesn't look like the kind of thing that Windows would be happy with... Try it with backslashes instead:

system("c:\\IQapture\\dmon2_6_IHD -p2 c:\\IQapture\\mon_table_101_Tx8.txt 11 0 0");

If that still doesn't work, you quite likely have one of the following issues:

  • Your current working directory is wrong;
  • An environment variable is missing;
  • Your program is running with the wrong user permissions;
  • Your program is tying up a resource that the spawned process requires (eg you have not closed a file that it requires as input).

Upvotes: 3

aib
aib

Reputation: 46921

There are a lot of things to consider - the environment, the user running the program, the parent process and what's inherited... Take a look at the parameters to the CreateProcess function. Chances are your system call's invocation isn't matching the command line's (though that may not be the issue, simpler things are more likely.)

I'd advise working backwards from the error to rule out simple causes such as the environment, current directory, etc. before delving into such things as creation flags and security attributes.

Upvotes: 2

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