check if string exists in a file

问题

I have the following piece of code which opens a text file and reads all the lines in the file and storing it into a string array.

Which then checks if the string is present in the array. However the issue I'm facing is that whenever a string is found, it always shows "there is a match" as well as "there is no match". Any idea how to fix this?

check this code:

using (StreamReader sr = File.OpenText(path))
{
    string[] lines = File.ReadAllLines(path);
    for (int x = 0; x < lines.Length - 1; x++)
    {
        if (domain == lines[x])
        {
            sr.Close();
            MessageBox.Show("there is a match");
        }
    }
    if (sr != null)
    {
        sr.Close();
        MessageBox.Show("there is no match");
    }
}

回答1:

I would recommend seting and flag and checking it as follows...

using (StreamReader sr = File.OpenText(path))
{
    string[] lines = File.ReadAllLines(path);
    bool isMatch = false;
    for (int x = 0; x < lines.Length - 1; x++)
    {
        if (domain == lines[x])
        {
            sr.Close();
            MessageBox.Show("there is a match");
            isMatch = true;
        }
    }
    if (!isMatch)
    {
        sr.Close();
        MessageBox.Show("there is no match");
    }
}

Good Luck!

回答2:

Sounds overly complex, no reason to check by line or anything if you want to know if a string is present in a file. You can replace all of your code simply with :

if(File.ReadAllText(path).Contains(domain))
{
    MessageBox.Show("There is a match");
}

回答3:

Actually you don't need to read whole file into memory. There is File.ReadLines method which allows you enumerate file lines one by one, without reading whole file. You can create following method

private bool DomainExists(string domain)
{
    foreach(string line in File.ReadLines(path))
        if (domain == line)
            return true; // and stop reading lines

    return false;
}

Usage of this method looks like:

if (DomainExists(domain))
    MessageBox.Show("there is a match");
else
    MessageBox.Show("there is no match");

Also two side notes - you don't need StreamReader if you are reading lines with File.ReadAllLines (it creates reader internally). Just check - you even don't use sr variable anywhere. And second note - you don't need to manually close stream, if you wrapped it in using block. In that case stream will be disposed and closed automatically.

回答4:

Simplest way:

string content = File.ReadAllText(path);
if (content.IndexOf(domain) > -1)
{
   // domain exists
}
else
{
   // domain does not exist
}

and now to analyze your code:

1st, you are creating StreamReader instance, but you don't use it later in your code.

2nd, what if domain name has multiple occurrence in the file? In your code you will get multiple 'there is a match' in your code.

using (StreamReader sr = File.OpenText(path)) // you can remove this line
{
    string[] lines = File.ReadAllLines(path); // as you are not using it here
    for (int x = 0; x < lines.Length - 1; x++)
    {
        if (domain == lines[x])
        {
            sr.Close();
            MessageBox.Show("there is a match");
            hasMatch = true;
            break; // exit loop if found
        }
    }

    if (!hasMatch)
    {
        // there is no match
    }

    if (sr != null) // you dont need this if you remove it from the beginning of the code
    {
        sr.Close();
        MessageBox.Show("there is no match");
    }
}

回答5:

You could try this code:

 using (StreamReader sr = File.OpenText(path))
                        {
                            string[] lines = File.ReadAllLines(path);
                            for (int x = 0; x < lines.Length - 1; x++)
                            {
                                if (lines[x].Contains(domain, StringComparison.InvariantCultureIgnoreCase)
                                {
                                    sr.Close();
                                    MessageBox.Show("there is a match");
                                }
                            }
                            if (sr != null)
                            {
                                sr.Close();
                                MessageBox.Show("there is no match");
                            }
                        }

回答6:

Try try catch:

string x;

string log = @"C:\Users\Log.txt";

string ruta = @"C:\Users\x.txt";

if (File.Exists(ruta))
{                    
    try
    {
        x = File.ReadAllText(ruta);  
    }
    catch (Exception ex)
    {
        File.AppendAllText(ruta, "Something");
        File.AppendAllText(log, Environment.NewLine + DateTime.Now.ToString() + ": The file not contain a string. " + ex.Message);
    }
}

来源：https://stackoverflow.com/questions/20309269/check-if-string-exists-in-a-file

标签

string

streamreader