- Indexing Direction in Arrays, Buffers and Timeseries
- Organizing Data Access
The function gets into volume_array the history data of trade volumes for the selected symbol-period pair in the specified quantity. It should be noted that elements ordering is from present to past, i.e., starting position of 0 means the current bar.
When copying the yet unknown amount of data, it is recommended to use dynamic array as a target array, because if the requested data count is less (or more) than the length of the target array, function tries to reallocate the memory so that the requested data fit entirely.
If you know the amount of data you need to copy, it should better be done to a statically allocated buffer, in order to prevent the allocation of excessive memory.
No matter what is the property of the target array - as_series=true or as_series=false. Data will be copied so that the oldest element will be located at the start of the physical memory allocated for the array. There are 3 variants of function calls.
Call by the first position and the number of required elements
Call by the start date and the number of required elements
Call by the start and end dates of a required time interval
[in] Symbol name.
[in] The start position for the first element to copy.
[in] Data count to copy.
[in] The start time for the first element to copy.
[in] Bar time, corresponding to the last element to copy.
[out] Array of long type.
Returns the copied data count or -1 in the case of error.
If the whole interval of requested data is out of the available data on the server, the function returns -1. If data outside TERMINAL_MAXBARS (maximal number of bars on the chart) is requested, the function will also return -1.
When requesting data from the indicator, if requested timeseries are not yet built or they need to be downloaded from the server, the function will immediately return -1, but the process of downloading/building will be initiated.
When requesting data from an Expert Advisor or script, downloading from the server will be initiated, if the terminal does not have these data locally, or building of a required timeseries will start, if data can be built from the local history but they are not ready yet. The function will return the amount of data that will be ready by the moment of timeout expiration, but history downloading will continue, and at the next similar request the function will return more data.
When requesting data by the start date and the number of required elements, only data whose date is less than (earlier) or equal to the date specified will be returned. It means, the open time of any bar, for which value is returned (volume, spread, value on the indicator buffer, prices Open, High, Low, Close or open time Time) is always less or equal to the specified one.
When requesting data in a specified range of dates, only data from this interval will be returned. The interval is set and counted up to seconds. It means, the open time of any bar, for which value is returned (volume, spread, value on the indicator buffer, prices Open, High, Low, Close or open time Time) is always within the requested interval.
Thus, if the current day is Saturday, at the attempt to copy data on a week timeframe specifying start_time=Last_Tuesday and stop_time=Last_Friday the function will return 0, because the open time on a week timeframe is always Sunday, but one week bar does not fall into the specified interval.
If you need to return value corresponding to the current uncompleted bar, you can use the first form of call specifying start_pos=0 and count=1.
See an example of history data requesting in section Methods of Object Binding. The script available in that section shows how to get the values of indicator iFractals on the last 1000 bars and how to display the last 10 up and 10 down fractals on the chart. A similar technique can be used for all indicators that have missing data and that are usually drawn using the following styles: