2

The compiler keeps whining about the need of a constant for the case type in a switch(){...}. But I have provided a freaking constant. - sorry, /rant mode off

Up in my class I have defined the type plus the TYPE_BULLISH and TYPE_BEARISH constants of the int types. Then I assigned values:

static const int TYPE_BULLISH = 0x001;
static const int TYPE_BEARISH = 0x002;

And I assigned the variable type a value of:

type = TYPE_BULLISH;

Then in the constructor 

switch(type) {
    case TYPE_BULLISH: Print("Bullish"); break;
    case TYPE_BEARISH: Print("Bearish"); break;
    default:           Print("Doji");
}

Output error:

'TYPE_BULLISH' - constant expression required

Q1: Any idea what is going on here?

I mean,
Q2: I provided a constant, right?

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2 Answers 2

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3

Try to use #define instead (note: No ; at the end of #define):

#define TYPE_BULLISH    0x001
#define TYPE_BEARISH    0x002
int type = TYPE_BULLISH;

switch(type) {
    case TYPE_BULLISH: Print("Bullish"); break;
    case TYPE_BEARISH: Print("Bearish"); break;
    default:           Print("Doji");
}
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3 Comments

Thanks, is this global or does it apply to the current class only?
@Nique, your issue is a syntactic-error. Your code snippets, as you have described above, ignore MQL4 scope-of-validity. #define just hides that principal misconcept of a proper structured-software design.
@Nique: It is Global-scoped. It is quite commonly used. You can see #define being used by many of the built-in MT4 sample/utilities. For example: stderror.mqh, stdliberr.mqh, winuser32.mqh, etc. #define is being used all the time.
1

A2: No, you have not provided a constant.

A1: Your MQL4 code is syntactically wrong and cannot get compiled.

While @JosephLee has provided a error-avoiding substitute, the problem is hidden in a way, MQL4-code retains a scope-of-validity

Your class-level designations cease to exist outside the container, where these have been declared / initialised.

Your code, outside of such container ( typically the inner-most surrounding { ... }-code block / hierarchy-level, where such a declaration took place ) simply cannot get compiled, as the compiler obeys the rules of scope-of-validity during the source-code parsing.

Q.E.D.

One may use "globally"-visible variables in case of a need for such centrally managed predefined constants.

Beware, that #include, #import, #property library and #export introduce more havoc into this circus.

You were warned, at least...

A use of a utility-function:

enter image description here

Example code how to use it from one library project:

enter image description here

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4 Comments

So basically, the Switch() case is useless unless you hardcode the to be matches values over and over again all over the place? Seems weird :).
@Nique btw, if you need not some artificial magic with a fixed memory location data-mapper, bypassing a stack-allocation mechanics, for some pretty nasty things, a static const int ... has no reason for storing a value. ( #define is a pre-compiler parsing directive, so actually no scope-checking takes place, just a lexer sequential code-stream analysis, so be carefull just about overlapping values & a global Project unique-error-number catalogue maintenance as in example -- #define anotherErrorNUMBER HAUSNUMERO + 161 ( a trick seen from Pieter Hintjens' code foundry :o) ).
Hmm #define is not the way to go i think. I want to keep the stuff inside the class scope. No need for global.
@Nique just for clarity, as you 've asked in first comment, #define <aLiteralSymbol> <aValue> are pre-processor directives and are thus lexically interpreted for the whole rest of the source-code file, ignoring any code-unit hierarchy & encapsulation, this a simple #include ... may help you in the very same manner as the .h header files do in C.

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