CODEWITHSUNDEEP
c++c++11
Captain n00b
Captain n00b

Reputation: 63

Getting the string(s) output from an exec command in C++

My problem is pretty simple, but I can't seem to find anything straightforward or specific to what I am trying to do. I'm simply using execl to list the files in the current folder that follow the same pattern (ie, execl("ls nameOfFile*.txt")). What I want to do now is grab those file names so that I can loop through and get the data out of them. Is there a simple way of doing this? Am I using the correct exec?

Thanks for any help or tips.

Upvotes: 0

Views: 399

Answers (1)

Praetorian
Praetorian

Reputation: 109189

The signature of execl is

int execl(const char *path, const char *arg, ...);

You're supposed to pass the path to the executable as the first argument, and arguments for the executable as the subsequent arguments, so your calling syntax is wrong. Even if you fix that, it still won't do what you want. The only way execl and friends ever return control to the calling program is if an error occurs. This answer contains an excellent explanation of what execl does.

You were probably thinking of std::system, which you can pass an arbitrary string to, and have the OS execute that command. While that'll print the filenames to stdout, it's still not what you want, because system returns an error code resulting from executing the command line you specified, it has no way of capturing and returning whatever may be written to stdout by the command.

Unfortunately, there is nothing in the C++ standard library (yet) that allows you to list and iterate files from the filesystem. The preferred cross platform approach is to use Boost.Filesystem. Otherwise, there are platform specific APIs available, which are listed in this answer, along with a Boost usage example.

Upvotes: 1

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