CA1305: Specify IFormatProvider

#Cause

A call is made to a method that has an overload that accepts a System.IFormatProvider argument, and that overload isn't called.

This rule ignores calls to .NET methods that are documented as ignoring the System.IFormatProvider parameter. The rule also ignores the following methods:

• System.Activator.CreateInstance
• System.Resources.ResourceManager.GetObject
• System.Resources.ResourceManager.GetString
• System.Boolean.ToString
• System.Char.ToString
• System.Guid.ToString

#Rule description

When a System.Globalization.CultureInfo or System.IFormatProvider object is not supplied, the default value that's supplied by the overloaded member might not have the effect that you want in all locales. Also, .NET members choose default culture and formatting based on assumptions that might not be correct for your code. To make sure that the code works as expected for your scenarios, you should supply culture-specific information according to the following guidelines:

• If the value will be displayed to the user, use the current culture. See System.Globalization.CultureInfo.CurrentCulture.

• If the value will be stored and accessed by software (persisted to a file or database), use the invariant culture. See System.Globalization.CultureInfo.InvariantCulture.

• If you don't know the destination of the value, have the data consumer or provider specify the culture.

Even if the default behavior of the overloaded member is appropriate for your needs, it's better to explicitly call the culture-specific overload so that your code is self-documenting and more easily maintained.

#How to fix violations

To fix a violation of this rule, use the overload that takes an System.IFormatProvider argument. Or, to use the invariant culture, use a C# interpolated string and pass it to System.String.Create(System.IFormatProvider,System.Runtime.CompilerServices.DefaultInterpolatedStringHandler@) along with System.Globalization.CultureInfo.InvariantCulture, for example:

string.Create(CultureInfo.InvariantCulture, $"{major}.{minor}.{build}.{revision}");

#When to suppress warnings

It is safe to suppress a warning from this rule when it is certain that the default format is the correct choice, and where code maintainability is not an important development priority.

#Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA1305
// The code that's violating the rule is on this line.
#pragma warning restore CA1305

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA1305.severity = none

For more information, see How to suppress code analysis warnings.

#Configure code to analyze

Use the following options to configure which parts of your codebase to run this rule on.

• Exclude specific symbols
• Exclude specific types and their derived types

You can configure these options for just this rule, for all rules they apply to, or for all rules in this category (Globalization) that they apply to. For more information, see Code quality rule configuration options.

#Exclude specific symbols

You can exclude specific symbols, such as types and methods, from analysis by setting the excluded_symbol_names option. For example, to specify that the rule should not run on any code within types named MyType, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType

Allowed symbol name formats in the option value (separated by |):

• Symbol name only (includes all symbols with the name, regardless of the containing type or namespace).
• Fully qualified names in the symbol's documentation ID format. Each symbol name requires a symbol-kind prefix, such as M: for methods, T: for types, and N: for namespaces.
• .ctor for constructors and .cctor for static constructors.

Examples:

#Exclude specific types and their derived types

You can exclude specific types and their derived types from analysis by setting the excluded_type_names_with_derived_types option. For example, to specify that the rule should not run on any methods within types named MyType and their derived types, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = MyType

Allowed symbol name formats in the option value (separated by |):

• Type name only (includes all types with the name, regardless of the containing type or namespace).
• Fully qualified names in the symbol's documentation ID format, with an optional T: prefix.

Examples:

#Example

In the following code, the example1 string violates rule CA1305. The example2 string satisfies rule CA1305 by passing System.Globalization.CultureInfo.CurrentCulture, which implements System.IFormatProvider, to System.String.Format(System.IFormatProvider,System.String,System.Object). The example3 string satisfies rule CA1305 by passing an interpolated string to System.String.Create(System.IFormatProvider,System.Runtime.CompilerServices.DefaultInterpolatedStringHandler@) along with System.Globalization.CultureInfo.InvariantCulture.

string name = "Georgette";

// Violates CA1305
string example1 = string.Format("Hello {0}", name);

// Satisfies CA1305
string example2 = string.Format(CultureInfo.CurrentCulture, "Hello {0}", name);

// Satisfies CA1305
string example3 = string.Create(CultureInfo.InvariantCulture, $"Hello {name}");

#Related rules

• CA1304: Specify CultureInfo

#See also

• Use the CultureInfo class