how to properly call an executable from C code?

remy06 · 05-13-2009, 09:41 AM

Hi,

I have an external executable program( eg. prog.exe) that I will like to call from within my main program consisting of C code.

prog.exe will do some work and prints the output to a temp.txt file for my main program to use for analysis later.

Currently I have a function like:

Code:

int dowork()
{
     ......
     int retv;

     //in command prompt it is executed as C:> prog.exe options
     retv = system("prog.exe options");  
     if(retv != 0)
         return 1;
}

So far it is able to print the results to the text file. However there are issues which I need some advice.

1. My main program that calls prog.exe is a GUI program.If I call it this way a command prompt window will pop-up promptly then closes,which I think not so nice to be like this. Therefore,is there another better way which I can do the same without having the command prompt window popping up and close?

2. I need to ensure also that prog.exe has finished writing to the text file before my main program reads the file.Will there be any issue using system()?

3. How can I properly check if prog.exe has been executed successfully or having errors,since it is an external executable program?

fyi,I am using windows xp and mingw.
Thanks in advanced.

**Salem** · 05-13-2009, 10:20 AM

You need to use something with a bit more control for your actual OS
Cprogramming.com FAQ > Run a program from within a program

system(), whilst portable, is pretty stupid and offers no actual control over what happens next.

> 3. How can I properly check if prog.exe has been executed successfully or having errors,since it is an external executable program?
Well if the programmer of prog.exe was a "void main" dimwit, you're screwed.
But if it returns a proper success/fail status, then you'll be able to get that and work out whether it succeeded or not.

> 2. I need to ensure also that prog.exe has finished writing to the text file before my main program reads the file
Wait for it to exit, which system() does.
But unlike on real operating systems, the system() function rarely returns the actual exit status of the called program (more often than not, you just get the exit status of the shell).

Like I said, use something like CreateProcess to get detailed control and a useful status back.

nonoob · 05-13-2009, 04:07 PM

How about

Code:

_spawnl(P_WAIT, path, path, filename, buffer, NULL);

(Microsoft Visual Studio C++)
I believe it returns whatever the executable program returns as a condition code.

Alex31 · 05-14-2009, 03:48 AM

system() is crappy and must not never be called
Use any Win32 api (ShellExecute, CreateProcess, etc... (some dozens))

05-13-2009, 09:41 AM	#1
remy06 Registered User Join Date: May 2009 Posts: 3	how to properly call an executable from C code? Hi, I have an external executable program( eg. prog.exe) that I will like to call from within my main program consisting of C code. prog.exe will do some work and prints the output to a temp.txt file for my main program to use for analysis later. Currently I have a function like: Code: int dowork() { ...... int retv; //in command prompt it is executed as C:> prog.exe options retv = system("prog.exe options"); if(retv != 0) return 1; } So far it is able to print the results to the text file. However there are issues which I need some advice. 1. My main program that calls prog.exe is a GUI program.If I call it this way a command prompt window will pop-up promptly then closes,which I think not so nice to be like this. Therefore,is there another better way which I can do the same without having the command prompt window popping up and close? 2. I need to ensure also that prog.exe has finished writing to the text file before my main program reads the file.Will there be any issue using system()? 3. How can I properly check if prog.exe has been executed successfully or having errors,since it is an external executable program? fyi,I am using windows xp and mingw. Thanks in advanced.
remy06 is offline

05-13-2009, 10:20 AM	#2
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,650	You need to use something with a bit more control for your actual OS Cprogramming.com FAQ > Run a program from within a program system(), whilst portable, is pretty stupid and offers no actual control over what happens next. > 3. How can I properly check if prog.exe has been executed successfully or having errors,since it is an external executable program? Well if the programmer of prog.exe was a "void main" dimwit, you're screwed. But if it returns a proper success/fail status, then you'll be able to get that and work out whether it succeeded or not. > 2. I need to ensure also that prog.exe has finished writing to the text file before my main program reads the file Wait for it to exit, which system() does. But unlike on real operating systems, the system() function rarely returns the actual exit status of the called program (more often than not, you just get the exit status of the shell). Like I said, use something like CreateProcess to get detailed control and a useful status back. __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

05-13-2009, 04:07 PM	#3
nonoob Registered User Join Date: Sep 2008 Location: Toronto, Canada Posts: 518	How about Code: _spawnl(P_WAIT, path, path, filename, buffer, NULL); (Microsoft Visual Studio C++) I believe it returns whatever the executable program returns as a condition code.
nonoob is offline

05-14-2009, 03:48 AM	#4
Alex31 Registered User Join Date: Apr 2007 Posts: 136	system() is crappy and must not never be called Use any Win32 api (ShellExecute, CreateProcess, etc... (some dozens))
Alex31 is offline

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