headers_list
http_response_code
Funções da Network
PHP Manual

# headers_sent

(PHP 4, PHP 5)

headers_sent — Checks if or where headers have been sent

### Descrição

bool headers_sent ([ string `&$file` [, int `&$line` ]] )

Checks if or where headers have been sent.

You can't add any more header lines using the header() function once the header block has already been sent. Using this function you can at least prevent getting HTTP header related error messages. Another option is to use Output Buffering.

### Parâmetros

`file`

  If the optional `file` and `line` parameters are set, headers_sent() will put the PHP source file name and line number where output started in the `file` and `line` variables.

`line`

  The line number where the output started.

### Valor Retornado

headers_sent() will return `FALSE` if no HTTP headers have already been sent or `TRUE` otherwise.

### Changelog

Versão | Descrição
--- | ---
4.3.0 | The optional `file` and `line` parameters were added.

### Exemplos

Exemplo #1 Examples using headers_sent()

`<?php
// If no headers are sent, send one
if (!headers_sent()) {
header('Location: http://www.example.com/');
exit;
}
// An example using the optional file and line parameters, as of PHP 4.3.0
// Note that $filename and $linenum are passed in for later use.
// Do not assign them values beforehand.
if (!headers_sent($filename, $linenum)) {
header('Location: http://www.example.com/');
exit;
// You would most likely trigger an error here.
} else {
echo "Headers already sent in $filename on line $linenum\n" .
"Cannot redirect, for now please click this <a " .
"href=\"http://www.example.com\">link</a> instead\n";
exit;
}
?>`

### Notas

> Nota:

> Headers só serão acessíveis e retornados quando a SAPI que os suporta estiver em uso.

### Veja Também

- ob_start() - Ativa o buffer de saída
- trigger_error() - Gera uma mensagem a nível de usuário de erro/aviso/notícia
- headers_list() - Returns a list of response headers sent (or ready to send)
- header() - Send a raw HTTP header for a more detailed discussion of the matters involved.

headers_list
http_response_code
Funções da Network
PHP Manual