PHP用CURL访问远程URL出现：Cannot modify header information...错误

<code>        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);  //请求URL
        curl_setopt($ch, CURLOPT_HEADER, 0);  //禁止输出头部信息
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); //获取信息以文件流的格式返回
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
        if( !is_null($postData) ){
            curl_setopt($ch, CURLOPT_POST, 1);  //POST提交
            curl_setopt($ch, CURLOPT_POSTFIELDS, $postData);
        }
        $return = curl_exec($ch);
        curl_close($ch);
        return $return;</code>

<code>Cannot modify header information - headers already sent by...</code>

<code>        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);  //请求URL
        curl_setopt($ch, CURLOPT_HEADER, 0);  //禁止输出头部信息
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); //获取信息以文件流的格式返回
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
        if( !is_null($postData) ){
            curl_setopt($ch, CURLOPT_POST, 1);  //POST提交
            curl_setopt($ch, CURLOPT_POSTFIELDS, $postData);
        }
        $return = curl_exec($ch);
        curl_close($ch);
        return $return;</code>

<code>Cannot modify header information - headers already sent by...</code>