Parsing of file with Key value in C/C++ - c++

Question

Need some help in parsing the file
Device# Device Name Serial No. Active Policy Disk# P.B.T.L ALB
Paths
--------------------------------------------------------------------------------------- -------------------------------------
1 AB OPEN-V-CM 50 0BC1F1621 1 SQST Disk 2 3.1.4.0 N/A
2 AB OPEN-V-CM 50 0BC1F1605 1 SQST Disk 3 3.1.4.1 N/A
3 AB OPEN-V*2 50 0BC1F11D4 1 SQST Disk 4 3.1.4.2 N/A
4 AB OPEN-V-CM 50 0BC1F005A 1 SQST Disk 5 3.1.4.3 N/A
The above information is in devices.txt file and and i want to extract the device number corresponding to the disk no i input.
The disk number i input is just an integer (and not "Disk 2" as shown in the file).

Answer 1

Open the file and skip first 3 lines.
Start reading line by line from 4th line onward. You can get the device number easily as it is the first column.
To get the disk no, search through each line using the space character. When you encounter one space character it means you've gone past one column. Ignore the repeated spaces and continue this until you reach the disk no. You must handle the spaces in the column data separately if it exist.
Load the disk no and device no in to say a map and later you can use your input to query the device info from this map.

Answer 2

#include <sstream>
#include <fstream>
#include <iostream>
#include <cctype>
using namespace std;
int main(int argc, char* argv[])
{
int wantedDisknum = 4;
int finalDeviceNum = -1;
ifstream fin("test.txt");
if(!fin.is_open())
return -1;
while(!fin.eof())
{
string line;
getline(fin, line);
stringstream ss(line);
int deviceNum;
ss >> deviceNum;
if(ss.fail())
{
ss.clear();
continue;
}
string unused;
int diskNum;
ss >> unused >> unused >> unused >> unused >> unused >> unused >> unused >> diskNum;
if(diskNum == wantedDisknum)
{
finalDeviceNum = deviceNum;
break;
}
}
fin.close();
cout << finalDeviceNum << endl;
system("pause");
return 0;
}

Answer 3

In UNIX, you can easily achieve this using awk or other script lang.
cat Device.txt | awk '{if ( $1 == 2 ) print}'
In C++, you have to extract specific column using strtok and compare it with 'val' if it matches print that line.'

Answer 4

Assuming there is no "Disk" in any of the following columns:
1) Skip lines until you encounter '-' as the first character of a line, then skip that line too.
2) read a line
2.a) skip characters of the current line until isdigit(line[i]) function returns true, then read current character and characters following it into a temporary buffer until isdigit(line[i]) returns false. This is the device id.
2.b) Skip characters of the current line until you find a 'D'
2.b.i) match 'i', 's', 'k' characters, if any of them fails, go to 2.b
2.c) skip characters of the current line until isdigit(line[i]) function returns true, then read current character and characters following it into another buffer until isdigit(line[i]) returns false. This is the disk id.
3) print out both buffers

Answer 5

I don't have my Regular Expression cheat sheet handy, but I'm pretty sure it would be straightforward to run each line in the file through a regex that:
1) looks for a integer in the line
2) skips whitespace followed by text three times
3) matches characters one space and characters
Boost, Qt, and most other common C++ class libraries have a Regex parser for just this kind of thing.