I'm using this URL to fetch some content from a Quandl website:
https://www.quandl.com/api/v3/datasets/FRED/PAYEMS.csv?exclude_column_names=true&rows=1&api_key=my_api_key
The Quandl server returns in response to the above request a value of this:
2016-08-01, 144598.0
I need to use the value of 144598.0 within an MQL4 Script, so:
Q1. How do I fetch the content from the URL above to be used within an MQL4 Script?
A very helpful user from SO (https://stackoverflow.com/users/3666197/user3666197) provided the following script (original found at MQL4: Read single value from CSV) (a couple parts added in by myself) to help me achieve this, however, I couldn't get it to work:
// Code created with the help of Stack Overflow question
// https://stackoverflow.com/questions/39279634/mql4-read-single-value-from-csv/39284875#39284875
// Question by p.luck:
// https://stackoverflow.com/users/5551849/p-luck
// Answer by user3666197:
// https://stackoverflow.com/users/3666197/user3666197
void OnStart()
{
string cookie = NULL,
headers;
char post[],
result[];
int res;
/* TODO: *
* Must allow MT4 to access the server URL, *
* you should add URL "https://www.quandl.com/api/v3/datasets/FRED/PAYEMS.csv" *
* in the list of allowed URLs *
* ( MT4 -> Tools -> Options -> [Tab]: "Expert Advisors" ): */
string aDataSOURCE_URL = "https://www.quandl.com/api/v3/datasets/FRED/PAYEMS.csv";
string aDataSOURCE_API = "?exclude_column_names=true&rows=1&api_key=my_api_key";
//-- Create the body of the POST request for API specifications and API-authorization
ArrayResize( post,
StringToCharArray( aDataSOURCE_API, // string text |--> [in] String to copy.
post, // uchar &array[] <--| [out] Array of uchar type.
0, // int start = 0 |--> [in] Position from which copying starts. Default - 0.
WHOLE_ARRAY, // int count = -1 |--> [in] Number of array elements to copy. Defines length of a resulting string. Default value is -1, which means copying up to the array end, or till terminating '\0'. Terminating zero will also be copied to the recipient array, in this case the size of a dynamic array can be increased if necessary to the size of the string. If the size of the dynamic array exceeds the length of the string, the size of the array will not be reduced.
CP_UTF8 // uint cp = CP_ACP |--> [in] The value of the code page. For the most-used code pages provide appropriate constants.
)
- 1
);
//-- Reset the last error code
ResetLastError();
//-- Loading a html page from Quandl
int timeout = 5000; //-- Timeout below 1000 (1 sec.) is not enough for slow Internet connection
res = WebRequest( "POST", // const string method |--> [in] HTTP method.
aDataSOURCE_URL, // const string URL |--> [in] URL.
cookie, // const string cookie |--> [in] Cookie value.
NULL, // const string referrer |--> [in] Value of the Referer header of the HTTP request.
timeout, // int timeout |--> [in] Timeout in milliseconds.
post, // const char &data |--> [in] Data array of the HTTP message body
ArraySize( post ), // int data_size |--> [in] Size of the data[] array.
result, // char &result <--| [out] An array containing server response data.
headers // string &result_headers <--| [out] Server response headers.
);
//-- Check errors
if ( res == -1 )
{ Print( "WebRequest Error. Error code = ", GetLastError() ); //-- Perhaps the URL is not listed, display a message about the necessity to add the address
MessageBox( "Add the address '" + aDataSOURCE_URL + "' in the list of allowed URLs on tab 'Expert Advisors'", "Error", MB_ICONINFORMATION );
}
else //-- Load was successfull
{
PrintFormat( "The data has been successfully loaded, size = %d bytes.", ArraySize( result ) );
//-- parse the content ---------------------------------------
/*
"2016-08-01, 144598.0"
*/
//-- consume the content -------------------------------------
//...
}
}
I have added the URL of
https://www.quandl.com/api/v3/datasets/FRED/PAYEMS.csv
to the list of allowed URLs in MT4.
If I enable AutoTrading and drag the script, named (tutorial7), on to a chart of USDCAD,M1,
I get these messages within the Experts tab:
Script tutorial7 USDCAD,M1: loaded successfulytutorial7 USDCAD,M1: initializedtutorial7 USDCAD,M1: The data has been successfully loaded, size = 0 bytestutorial7 USDCAD,M1: uninit reason 0
Surely if the "The data has successfully loaded" it shouldn't say "size = 0 bytes"?
Should this script work correctly if I just copy and paste it straight in to the MetaQuotes Language Editor and compile it?
Apart from adding the URL to the allowed URLs in MT4 and copying and pasting this code in to a script, is there anything else I must do?
If so, how?
I am running the above code as a Script not an Expert Advisor; is this okay?
Q2. Can I set the fetched value of 144598.0 as a variable within my script?
I need to make the value of 144598.0 a variable so that it can be compared to another value.
Would something like this work:
void OnStart()
{
... // above code which fetches the value from the .csv URL
double x = 155876.0 // value manually typed in
y = 144598.0 // value fetched from the .csv URL using the above code
// ignores column 1 consisting of 2016-08-01
if ( x > y ) {
// execute code
}
else {
// execute other code
}
}
