Can I pass parameters to String.Format without specifying numbers?

Question

Is there a way to String.Format a message without having to specify {1}, {2}, etc? Is it possible to have some form of auto-increment? (Similar to plain old printf)

Answer 1

You can use a named string formatting solution, which may solve your problems.

Answer 2

Afraid not -- where would it put the objects into the string? Using printf, you still need to put specifiers in somewhere.

Answer 3

I think the best way would be passing the property names instead of Numbers. use this Method:

using System.Text.RegularExpressions;
using System.ComponentModel;

public static string StringWithParameter(string format, object args)
    {
        Regex r = new Regex(@"\{([A-Za-z0-9_]+)\}");

        MatchCollection m = r.Matches(format);

        var properties = TypeDescriptor.GetProperties(args);

        foreach (Match item in m)
        {
            try
            {
                string propertyName = item.Groups[1].Value;
                format = format.Replace(item.Value, properties[propertyName].GetValue(args).ToString());
            }
            catch
            {
                throw new FormatException("The string format is not valid");
            }
        }

        return format;
    }

Imagine you have a Student Class with properties like: Name, LastName, BirthDateYear and use it like:

 Student S = new Student("Peter", "Griffin", 1960);
 string str =  StringWithParameter("{Name} {LastName} Born in {BithDate} Passed 4th grade", S);

and you'll get: Peter Griffin born in 1960 passed 4th grade.

Answer 4

There is a C# implementation of printf available here

Answer 5

If someone is interested, I have modified Ashkan's solution to be able to run it under WinRT:

/// <summary>
/// Formats the log entry.
/// /// Taken from:
/// http://stackoverflow.com/questions/561125/can-i-pass-parameters-to-string-format-without-specifying-numbers
/// and adapted to WINRT
/// </summary>
/// <param name="format">The format.</param>
/// <param name="args">The arguments.</param>
/// <returns></returns>
/// <exception cref="System.FormatException">The string format is not valid</exception>
public static string FormatLogEntry(string format, object args)
{
    Regex r = new Regex(@"\{([A-Za-z0-9_]+)\}");

    MatchCollection m = r.Matches(format);

    var properties = args.GetType().GetTypeInfo().DeclaredProperties;

    foreach (Match item in m)
    {
        try
        {
            string propertyName = item.Groups[1].Value;
            format = format.Replace(item.Value, properties.Where(p=>p.Name.Equals(propertyName))
                .FirstOrDefault().GetValue(args).ToString());
        }
        catch
        {
            throw new FormatException("The string format is not valid");
        }
    }

    return format;
}

Answer 6

One could always use this (untested) method, but I feel it's over complex:

public static string Format(char splitChar, string format,
                            params object[] args)
{
    string splitStr = splitChar.ToString();
    StringBuilder str = new StringBuilder(format + args.Length * 2);
    for (int i = 0; i < str.Length; ++i)
    {
        if (str[i] == splitChar)
        {
            string index = "{" + i + "}";
            str.Replace(splitStr, index, i, 1);
            i += index.Length - 1;
        }
    }

    return String.Format(str.ToString(), args);
}

Answer 7

I came up with this, again it's a bit cumbersome but it works fine for what I needed to do which was to pass a variable number or arguments to my own function in the same way as I'd use WriteLine. I hope it helps somebody

protected void execute(String sql, params object[] args)
{
    for (int i = 0; i < args.Count(); i++ )
    {
        sql = sql.Replace(String.Format("{{{0}}}", i), args[i].ToString());
    }
    //...
}