CA2017: Parameter count mismatch

Cause

The number of parameters supplied in the logging message template does not match the number of named placeholders.

Rule description

This rule flags logger calls that have an incorrect number of message arguments.

How to fix violations

Match the number of placeholders in the template format with the number of passed arguments.

When to suppress warnings

Do not suppress a warning from this rule.

Example

The following example shows methods that violate CA2017 and methods that satisfy the rule.

public class LoggingExample
{
    private readonly ILogger<LoggingExample> _logger;

    public LoggingExample(ILogger<LoggingExample> logger)
    {
        _logger = logger;
    }

    public void ExampleMethod()
    {
        string name = "Alice";
        int age = 30;

        // Violates CA2017: Too few arguments for placeholders.
        _logger.LogInformation("User {Name} is {Age} years old and lives in {City}", name, age);

        // Violates CA2017: Too many arguments for placeholders.
        _logger.LogError("Error occurred: {Message}", "Something went wrong", "Extra argument");

        // Correct usage: Matching number of placeholders and arguments.
        _logger.LogInformation("User {Name} is {Age} years old", name, age);
    }
}

Imports Microsoft.Extensions.Logging

Public Class LoggingExample

    Private ReadOnly _logger As ILogger(Of LoggingExample)

    Public Sub New(logger As ILogger(Of LoggingExample))
        _logger = logger
    End Sub

    Public Sub ExampleMethod()
        Dim name As String = "Alice"
        Dim age As Integer = 30

        ' Violates CA2017: Too few arguments for placeholders.
        _logger.LogInformation("User {Name} is {Age} years old and lives in {City}", name, age)

        ' Violates CA2017: Too many arguments for placeholders.
        _logger.LogError("Error occurred: {Message}", "Something went wrong", "Extra argument")

        ' Correct usage: Matching number of placeholders and arguments.
        _logger.LogInformation("User {Name} is {Age} years old", name, age)
    End Sub

End Class

See also

• Reliability rules