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CA1305: Specify IFormatProvider

  • Article
Property Value
Rule ID CA1305
Title Specify IFormatProvider
Category Globalization
Fix is breaking or non-breaking Non-breaking
Enabled by default in .NET 8 No

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 IFormatProvider parameter. The rule also ignores the following methods:

Rule description

When a System.Globalization.CultureInfo or 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 CultureInfo.CurrentCulture.

  • If the value will be stored and accessed by software (persisted to a file or database), use the invariant culture. See 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 IFormatProvider argument. Or, to use the invariant culture, use a C# interpolated string and pass it to String.Create(IFormatProvider, DefaultInterpolatedStringHandler) along with 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.

You can configure these options for just this rule, for all rules it applies to, or for all rules in this category (Globalization) that it applies 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. 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:

Option Value Summary
dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType Matches all symbols named MyType.
dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType1|MyType2 Matches all symbols named either MyType1 or MyType2.
dotnet_code_quality.CAXXXX.excluded_symbol_names = M:NS.MyType.MyMethod(ParamType) Matches specific method MyMethod with the specified fully qualified signature.
dotnet_code_quality.CAXXXX.excluded_symbol_names = M:NS1.MyType1.MyMethod1(ParamType)|M:NS2.MyType2.MyMethod2(ParamType) Matches specific methods MyMethod1 and MyMethod2 with the respective fully qualified signatures.

Exclude specific types and their derived types

You can exclude specific types and their derived types from analysis. 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:

Option Value Summary
dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = MyType Matches all types named MyType and all of their derived types.
dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = MyType1|MyType2 Matches all types named either MyType1 or MyType2 and all of their derived types.
dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = M:NS.MyType Matches specific type MyType with given fully qualified name and all of its derived types.
dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = M:NS1.MyType1|M:NS2.MyType2 Matches specific types MyType1 and MyType2 with the respective fully qualified names, and all of their derived types.

Example

In the following code, the example1 string violates rule CA1305. The example2 string satisfies rule CA1305 by passing CultureInfo.CurrentCulture, which implements IFormatProvider, to String.Format(IFormatProvider, String, Object). The example3 string satisfies rule CA1305 by passing an interpolated string to String.Create(IFormatProvider, DefaultInterpolatedStringHandler) along with 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}");

See also