# V3057. Function receives an odd argument.

The analyzer detected a possible error that has to do with passing a suspicious value as an argument to a function.

Consider the following examples:

Invalid characters in a path

    string GetLogPath(string root)
    {
      return System.IO.Path.Combine(root, @"\my|folder\log.txt");
    }

A path containing invalid character '|' is passed to function 'Combine()'. It will result in an 'ArgumentException'.

The fixed version:

    string GetLogPath(string root)
    {
      return System.IO.Path.Combine(root, @"\my\folder\log.txt");
    }

Suspicious argument to format function

    string.Format(mask, 1, 2, mask);

The 'string.Format()' function replaces one or more format items in a specified string. An attempt to write the same string into the format string is treated as suspicious by the analyzer.

Invalid index

    var pos = mask.IndexOf('\0');
    if (pos != 0)
        asciiname = mask.Substring(0, pos);

'IndexOf()' returns the position of a specified argument. If the argument is not found, the function returns the value '-1'. And passing a negative index to function 'Substring()' results in an 'ArgumentOutOfRangeException'.

The fixed version:

    var pos = mask.IndexOf('\0');
    if (pos > 0)
        asciiname = mask.Substring(0, pos);

Note that the analyzer may also issue a warning when a correct argument is passed to the method, but the corresponding parameter inside the method may take an invalid value.

    static void Bar(string[] data, int index, int length)
    {
      if (index < 0)
        throw new Exception(....);

      if (data.Length < index + length)
        length = data.Length - index;             // <=

      ....
      Array.Copy(data, index, result, 0, length); // <=
    }

    static void Foo(string[] args)
    {
      Bar(args, 4, 2);                            // <=
      ....
    }

In this case, the analyzer will issue a warning that the 'length' parameter used in the 'Array.Copy' method call may take a negative value. This parameter corresponds to the '2' argument passed in the 'Bar' call. This will result in 'ArgumentOutOfRangeException'.

Indeed, if the size of the 'args' array ('data' inside the 'Bar' method) is less than 4, a negative value will be written to 'length' inside 'Bar', despite the fact that a positive value (2) is passed to the method. As a result, an exception will be thrown when calling 'Array.Copy'.

In the 'Bar' method, you should add a check for the new 'length' value and the necessary processing of negative values:

    if (data.Length < index + length)
      length = data.Length - index;

    if (length < 0)
      .... // Error handling

This diagnostic is classified as:

CWE-628

You can look at examples of errors detected by the V3057 diagnostic.