Descriptive symbol properties

The platform provides a group of text properties for MQL programs that describe important qualitative characteristics. For example, when developing indicators or trading strategies based on a basket of financial instruments, it may be necessary to select symbols by country of origin, economic sector, or name of the underlying asset (if the instrument is a derivative).

Another case where the program can apply the analysis of these properties occurs when looking for a conversion rate from one currency to another. We already know how to find a symbol with the right combination of base and quote currency, but the difficulty is that there may be several such symbols. Reading properties like SYMBOL_SECTOR_NAME (you need to look for "Currency" or a synonym; check with your broker's specification) or SYMBOL_PATH can help in such cases.

The SYMBOL_PATH contains the entire hierarchy of folders in the symbols directory that contain the specific symbol: folder names are separated by backslashes ('\\') in the same way as the file system. The last element of the path is the name of the symbol itself.

Some string properties have integer counterparts. In particular, instead of SYMBOL_SECTOR_NAME, you can use the SYMBOL_SECTOR property, which returns an enumeration member ENUM_SYMBOL_SECTOR with all supported sectors. By analogy, for SYMBOL_INDUSTRY_NAME there is a similar property SYMBOL_INDUSTRY with the ENUM_SYMBOL_INDUSTRY enumeration type.

If necessary, an MQL program can even find the background color used when displaying a symbol in the Market Watch by simply reading the SYMBOL_BACKGROUND_COLOR property. This will allow those programs that create their own interface on the chart using graphic objects (dialog boxes, lists, etc.), to make it unified with the native terminal controls.

Consider the example script SymbolFilterDescription.mq5, which outputs four predefined text properties for Market Watch symbols. The first of them is SYMBOL_DESCRIPTION (not to be confused with the name of the symbol itself), and it is by it that the resulting list will be sorted. The other three are purely for reference: SYMBOL_SECTOR_NAME, SYMBOL_COUNTRY, SYMBOL_PATH. All values are filled in in a specific way for each broker (there may be discrepancies for the same ticker).

We haven't mentioned it, but our SymbolFilter class implements a special overload of the equal method to compare strings. It supports searching for the occurrence of a substring with a pattern in which the wildcard character '*' stands for 0 or more arbitrary characters. For example, "*ian*" will find all characters that contain the substring "ian" (anywhere), and "*Index" will only find strings ending in "Index".

This feature resembles a substring search in the Symbols dialog available to users. However, there is no need to specify a wildcard character, because a substring is always searched for. In the algorithm which can be found in the source codes (SymbolFilter.mqh), we left the possibility to search for either a full match (there are no '*' characters) or a substring (there is at least one asterisk).

The comparison is case-sensitive. If necessary, it is easy to adapt the code for comparison without distinguishing between lowercase and uppercase letters.

Given the new feature, let's define an input variable for the search string in the description of the symbols. If the variable is empty, all symbols from the Market Watch window will be displayed.

Further, everything is as usual.

Here is a possible version of the list (with abbreviations).

If we enter the search string "*ian*" into the input variable SearchPattern, we get the following result.