Communicate PHP with Postgresql

Question

I’m trying to communicate a program made in php with postgresql bd. I made a connected class, as shown below:

<?php
class conexao{

var $connect;
var $con_string = "host=localhost/TCC port=5432 dbname=TCC user=postgres  password=123456";


function conexao(){
$this->connect = pg_connect($this->con_string);
}

function executarSQL($sql){
return pg_query($this->connect, $sql);
}

function prepararString($texto){
return '\''.$texto.'\'';
}


}
?>

and This is the class of index.php:

<?php
//session_start();
include ("classes/conexao.php");
$postgresql=new conexao;


if(isset($_POST['usuario'])){
$usuario=$postgresql->converte($_POST['usuario']);
$senha=$postgresql->converte($_POST['senha']);
$sql= 'select * from usuario where usuario='.$postgresql-
>prepararString($usuario).' and senha='.$postgresql->prepararString($senha);

$result = $postgresql->executarSQL($sql);        
if (pg_num_rows($result) > 0){
    $_SESSION['usuario']=$usuario;
    header("Location: anexos/principal.php");
}else{
    echo "<center><font align='center' size='5' color='RED'>O NOME DE USUÁRIO E SENHA DIGITADOS SÃO INCORRETOS.</a></font></center><br>";


 }
}
else{
header("Location: login.php");
}

?>    

I put all the code inside the xampp folder, htdocs, and I can see the site, however, when it comes to communicating with the bd, it contains this error:

Fatal error: Uncaught Error: Call to Undefined Function pg_connect() in C: xampp htdocs TCC Course Completion Work TCC SYSTEM src related classes.php:9 Stack trace: #0 C: xampp htdocs TCC Course Completion Work TCC SYSTEM src index.php(41): connectedness->connectedness() #1 {main} thrown in C: xampp htdocs TCC Course Completion Work TCC SYSTEM src related classes.php on line 9

Can anyone help me with this problem??? Thank you!