Read the previous line of the text file; if the current line contains "X",
At this point I have a file that is being read for a specific record "X". Once I find this entry, I can do what I need to do on the following lines, but there is some information that takes 2 lines before the "X" appears. Right now I can use var line = reader.ReadLine();
to move forward in the file and read the lines that appear after the "X". How do I go back to read this data 2 lines earlier?
while (!reader.EndOfStream)
{
var line = reader.ReadLine();
if (line.Contains("X"))
{
Processing
}
}
Instead, StreamReader
you can use File.ReadAllLines
which returns a string array:
string[] lines = File.ReadAllLines("file.txt")
for (int i = 0; i < lines.Length; i++)
{
if (lines[i].Contains("X") && i >= 2)
{
string res = lines[i-2];
}
}
Save it as you go:
string prev1;
string prev2;
while (!reader.EndOfStream)
{
var line = reader.ReadLine();
if (line.Contains("X"))
{
Processing
}
prev2 = prev1;
prev1 = line;
}
If you need more this can easily be converted to a queue you push / pull on.
Just keep the last 2 lines.
Fixed size queue that automatically overrides old values with new parameters
Save the previous two lines:
string [] lineprev = new string[]{"",""} ;
while (!reader.EndOfStream)
{
var line = reader.ReadLine();
if (line.Contains("X"))
{
// Processing : Find info in lineprev[1]
}
lineprev[1]=lineprev[0] ;
lineprev[0]= line ;
}
Try to keep the previous line in memory so you can access it when you need it. Something like that:
var prev;
while (!reader.EndOfStream)
{
var line = reader.ReadLine();
if (line.Contains("X")) {
// Processing both line and prev
}
prev = line; // remember previous line for future use
}