API integration using PHP curl

Question

I am writing a script that does foreign exchange using an API to do it in realtime.

I presume that the problem is in my implementation of curl, as I get no output from this :

$currencyBase    = "USD";
$currencyForeign = "EUR";
$url             = 'https://www.alphavantage.co/query?function=CURRENCY_EXCHANGE_RATE&from_currency=' . $currencyBase . '&to_currency=' . $currencyForeign . '&apikey=KCUGBA9AP3Z1E2P8';

echo $currencyBase;

// create curl resource
$c = curl_init($url); //Initialize a cURL session
curl_setopt($c, CURLOPT_HEADER, 0);  //Set an option for a cURL transfer
curl_setopt($c, CURLOPT_RETURNTRANSFER, 1); //Set an option for a cURL transfer                           
$this->fxRate = doubleval(curl_exec($c));  
curl_close($c);  //Close a cURL session

I have hardcoded

$currencyBase    = "USD";
$currencyForeign = "EUR";

for debugging and I have also tried print_r($c) to see if I'm passing anything but I still get no output.

I know that my API call works because I have tried the link with entered USD and EUR and I get a response when I enter it in the browser as follows:

https://www.alphavantage.co/query?function=CURRENCY_EXCHANGE_RATE&from_currency=USD&to_currency=EUR&apikey=KCUGBA9AP3Z1E2P8

But I always get an empty response when I print the output from the script.

Are you decoding the result anywhere? That URL returns JSON for me, and you're trying to convert it to a float. — iainn
– iainn, Commented Nov 3, 2017 at 17:31
You should keep your API key private - maybe best to cancel and request a new one. I ran your copied code on my server to live test (unintentionally) with YOUR key (before Blues answer). — scytale
– scytale, Commented Nov 3, 2017 at 19:01
I am only using it for testing, but yes I will request a new one. Thank you! — sforg1
– sforg1, Commented Nov 3, 2017 at 19:09

blues · Accepted Answer · 2017-11-03 18:23:08Z

1

Your problem is this part of the code: $this->fxRate = doubleval(curl_exec($c));

curl_exec returns a string (which happens to be json), which you are casting to doubleval and that results in 0. Try it like this instead:

$this->fxRate = json_decode(curl_exec($c))->{"Realtime Currency Exchange Rate"}->{"5. Exchange Rate"};

answered Nov 3, 2017 at 18:23

blues

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