C++ system() function - How to collect the return value of the issued command?

Question

Hello,

I run some commands with the C++ system() function (int system ( const char * command );). How can I collect the return value of the issued commands?

EDIT: To be more specific: I want to collect the output of the issued command. i.e. the directory listing of the dir command.

Thanks,
mspoerr

Answer 1

system() returns an int, so just grab it: int rvalue = system(command);

I believe the exact details of what system() will return are system-specific, though.

Answer 2

system() is declared and defined in libc. You can either read the first link I provided, or do man system at a command prompt in your shell.

Answer 3

There are typically two ways for a system program to "return" a value: by writing to stdout, and by returning a status integer at the end of the program. (there are often more ways to return results, eg. by writing to a file or into a database, but I assume those are out of scope here).

For receiving the status code, just check the return value of the system function.

For receiving the output, either redirect it into a file, and read the file afterwards, or use popen.

Answer 4

Are you looking for returned value (as in "exit status") of the executed command, or for its output (as in "what did it print")?

If the latter, use popen(3) instead.

Answer 5

The return value of system is (ironically) system-dependent, but in POSIX systems (including Linux, etc), it's the same as for wait -- low 8 or 16 bits are the exit status of the child (probably what you mean by "value returned by"), higher bits indicating what kind of signal terminated the child, if any. The URL to the manpage I've given supplies the preprocessor macros you can use to pry apart that return value!

There is no such thing as a "return string" of a program, as you've now clarified in a comment is what you desire; as another answer already mentioned, if you want the text which gets output by the other program, you should use popen instead of system.

Answer 6

I suggest the popen() functions, as said by other people as well, but this problem is platform specific. the popen() function is available on operating systems that use the POSIX API. I am not sure if this command would work on other APIs like WIN32