# V3025. Incorrect format. Consider checking the N format items of the 'Foo' function.

The analyzer has detected a possible error related to use of formatting methods: String.Format, Console.WriteLine, Console.Write, etc. The format string does not correspond with actual arguments passed to the method.

Here are some simple examples:

Unused arguments.

    int A = 10, B = 20;
    double C = 30.0;
    Console.WriteLine("{0} < {1}", A, B, C);

Format item {2} is not specified, so variable 'C' won't be used.

Possible correct versions of the code:

    //Remove extra argument
    Console.WriteLine("{0} < {1}", A, B);

    //Fix format string
    Console.WriteLine("{0} < {1} < {2}", A, B, C);

Number of arguments passed is less than expected.

    int A = 10, B = 20;
    double C = 30.0;
    Console.WriteLine("{0} < {1} < {2}", A, B);
    Console.WriteLine("{1} < {2}", A, B);

A much more dangerous situation occurs when a function receives fewer arguments than expected. This will raise a FormatException exception.

Possible correct versions of the code:

    //Add missing argument
    Console.WriteLine("{0} < {1} < {2}", A, B, C);

    //Fix indices in format string
    Console.WriteLine("{0} < {1}", A, B);

The analyzer doesn't output the warning given that:

- The number of format items specified matches the number of arguments.
- The format object is used a number of times:

    int row = 10;
    Console.WriteLine("Line: {0}; Index: {0}", row);

Here is an example of this bug in a real-life application:

    var sql = string.Format(
      "SELECT {0} FROM (SELECT ROW_NUMBER() " +
      " OVER (ORDER BY {2}) AS Row, {0} FROM {3} {4}) AS Paged ",
      columns, pageSize, orderBy, TableName, where);

The function receives 5 formatting objects, but the 'pageSize' variable is not used as format item {1} is missing.

This diagnostic is classified as:

CWE-685

You can look at examples of errors detected by the V3025 diagnostic.