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# setValue(_:forHTTPHeaderField:)

Sets a value for the header field.

```
func setValue(_ value: String?, forHTTPHeaderField field: String)
```

## Parameters

`value`

The new value for the header field. Any existing value for the field is replaced by the new value.

`field`

The name of the header field to set. In keeping with the HTTP RFC, HTTP header field names are case insensitive.

## Discussion

Certain header fields are reserved. Do not use this method to set such headers. Specifically, there is no need for you to set the `Content-Length` header. See [`Reserved HTTP headers`](/documentation/Foundation/NSURLRequest#Reserved-HTTP-headers).

## See Also

[`-  valueForHTTPHeaderField:`](/documentation/Foundation/NSURLRequest/value(forHTTPHeaderField:))

Returns the value of the specified HTTP header field.


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