String.IndexOf is called and its result is compared against zero.
Rule descriptionIt's more efficient and clearer to call String.StartsWith than to call String.IndexOf and compare the result with zero to determine whether a string starts with a given prefix.
IndexOf
searches the entire string, while StartsWith
only compares at the beginning of the string.
Replace the call to String.IndexOf with a call to String.StartsWith.
ExampleThe following code snippet shows a violation of CA1858:
bool M(string s)
{
return s.IndexOf("abc") == 0;
}
Function M(s As String) As Boolean
Return s.IndexOf("abc") = 0
End Function
The following code snippet fixes the violation:
bool M(string s)
{
return s.StartsWith("abc");
}
Function M(s As String) As Boolean
Return s.StartsWith("abc")
End Function
When to suppress warnings
It's safe to suppress this warning if performance isn't a concern.
Suppress a warningIf 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 CA1858
// The code that's violating the rule is on this line.
#pragma warning restore CA1858
To disable the rule for a file, folder, or project, set its severity to none
in the configuration file.
[*.{cs,vb}]
dotnet_diagnostic.CA1858.severity = none
For more information, see How to suppress code analysis warnings.
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