How do you specify a line number with getline() (c++)

Question

How do you specify which line for getline() to read with c++ similiar to how awk uses $1, $2, $3 , etc etc...
Example:(Ignore the underscores)
Line1 Line2
10____10
20____20
30____30
40____40
if I were making a program to remove 10 on the first line and 20 on the second line how would I tell getline which line to read
Example source code:
#include <cstdio>
#include <fstream>
#include <string>
#include <iostream>
using namespace std;
int main()
string line;
string line2;
ifstream in("/Users/lundquisted/Desktop/infile.txt");
ofstream out("/Users/lundquisted/Desktop/outfile.txt");
while( getline(in,line) )
if(line != "10")
out << line << endl;
while (getline(in,line2) )
if(line2 != "20")
out << line2 << endl;
in.close();
out.close();
remove("/Users/lundquisted/Desktop/infile.txt");
rename("/Users/lundquisted/Desktop/outfile.txt","/Users/lundquisted/Desktop/inf ile.txt");
return 0;
}

Answer 1

Eric Lundquist wrote:
store the output of a system() command within a c++ program to a string and/or variable
A number of apps call Unix utilities and capture both stdout and stderr, typically for viewing in a log window, but for other uses as well. Xcode, for example, starts up gcc and does various things with the text that gcc might otherwise print in a Terminal window. Most apps that rely on Unix commands that way don't use "system()", which is a rather crude way of launching utilities that leaves the parent program with very little control. Usually, the best way to manage helper utils from a Cocoa app is by using NSTask and NSPipe. If you spend some time with the two following pages, you'll learn how to do almost anything you want with command line utils from inside a Cocoa app:
[http://www.cocoadevcentral.com/articles/000025.php]
[http://macosx.com/forums/archive/t-3927.html]
The first link goes to a great tutorial on using NSTask. Capturing stdout and stderr are only covered briefly towards the end, however. Note the last comment explaining why "system()" is a bad idea.
The second link goes to a forum thread. Scroll down to the code posted by "blb" for some very clear examples of launching with NSTask and reading the output with NSPipe.
If you really want to use a shell command, you could give NSTask a command like ' +bash -c "ls -lt | grep drwx"+ ' (see how setArguments: is used in the tutorial).
If you just want to do something cheap and dirty with "system()" so you can see some awk output while you're learning how to do things the right way, I guess you could do something like this:
system(" cat ~/random.txt | awk '{print $2}' > MyFile.txt");
NSString *myString = [NSString stringWithContentsOfFile:@"MyFile.txt"
encoding:NSUTF8StringEncoding error:nil];
Of course you can just read MyFile.txt into cin if you're not using Cocoa.
- Ray