Please please help with this simple Q from a C++ newbie

[meixiang6]

Please please help with this simple Q from a C++ newbie....I spent hours trying to find the answer online... I want to run this on a linux box. Open a file containing a list of file names and then run a linux commands on each of the list for example: The file contains a list of files names eg: test test1 test2 test3 How do I code in C so that it opens the file and then foreach of the elements do a system command eg: ls in perl it would be something like: #!/usr/local/bin/perl while(<>){ chomp; $cmd="ls $_"; system($cmd); print "$cmd\n"; } Thanks in advance!

[Stuart Dootson]

Use fgets to read individual lines from a file. Use strcat to append the file name to the command (just make sure the command is in a long enough string to start with). C has a system function just like Perl as well. It's easier in C++, using std::getline to read lines from a file and the std::string class to build the command:

#include <stdlib.h>
#include <iostream>
#include <fstream>
#include <string>

int main(int argc, char** argv)
{
std::ifstream f(argv[1]);

std::string s;
while (std::getline(f, s))
{
system((std::string("ls -l ") + s).c_str());
}
}

Easy enough (and works on OS X, which is close enough to Linux)

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

[meixiang6]

Thanks very much Stuart! Any chance of typing the entire code in C as well? thanks a lot again!

[Stuart Dootson]

meixiang6 wrote:

Any chance of typing the entire code in C as well?

I'll leave that as an exercise for the reader...you remember I said it was easier in C++ :-) It's not too much different - fgets is roughly equivalent to getline. Rather than adding string objects together, you use strcpy to copy the command into a character buffer, then strcat to add the line you've read from the file to the end of the buffer. Then you pass the buffer to the system command.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

[meixiang6]

thanks Stuart for the information, I am a very new newbie and have no idea how that looks like in C, any chance of someone writing that in C ? apologizes for the inconvenience

[Stuart Dootson]

You'll gain a lot more learning how to do it yourself. This page[^] has code that reads a file line by line (search for 'fgets').

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

[meixiang6]

Thanks Stuart, I got it working with this, not sure if the code is right thou but it works... #include #include int main() { FILE *f; char string[1000]; char str[1000]; f = fopen("file.txt", "r"); if(!f) { printf("Couldn't open file.txtn"); return 1; } while(fgets(str, 1000, f)) { /* printf("%s", str); */ strcpy (string, "ls -la "); strcat (string, str); system (string); } fclose(f); return 0; }

modified on Thursday, February 19, 2009 8:56 PM

[David Crow]

meixiang6 wrote:

char string[1000];

I know this is being nit-picky, but you might want to make this 7 bytes larger than str. If str contains 999 bytes, copying that plus "ls -la " is going to overflow string.

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[Stuart Dootson]

Aside from what David said, that code's fine :-)

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p