Use template to implement Conditional compilation

We know that Conditional compilation can be implemented using macros: # If 1
// Do something
# Else
// Do something else
# Endif

Using a template can achieve similar results: # include <stdio. h>

Template <bool value>
Void func ()
...{
If (value)
...{
Printf ("true ");
}
Else
...{
Printf ("false ");
}
}

Int main ()
...{
Func <true> ();
Return 1;
}

You may be worried that using if to determine whether it will affect performance. Let's look at the code generated by the compiler:
GCC compiler:
; G ++-O main. s main. cpp-S

. Globl _ z4funcilb1eevv . Def _ z4funcilb1eevv;. SCL 2;. Type 32;. endef _ Z4funcilb1eevv: Pushl % EBP Movl % ESP, % EBP Subl $8, % ESP Movl $ lc0, (% ESP) Call _ printf Leave RET . Def _ printf;. SCL 2;. Type 32;. endef . Def _ z4funcilb1eevv;. SCL 3;. Type 32;. endef

It can be seen that there is no conditional judgment in the generated code after GCC compilation.

Try again using Microsoft's Compiler:
; Call E:/win2003_program/vs2005/VC/bin/vcvars32.bat
; Cl.exe/Fas main. cpp

; Function compile flags:/odtp ; Comdat ?? $ Func @ $00 @ yaxxz _ Text Segment ?? $ Func @ $00 @ yaxxz proc; func <1>, comdat ; 5 :{ Push EBP MoV EBP, ESP ; 6: If (value) MoV eax, 1 Test eax, eax Je short $ ln2 @ func ; 7 :{ ; 8: printf ("True/N "); Push offset $ sg3676 Call _ printf Add ESP, 4 ; 9 :} ; 10: else JMP short $ Ln3 @ func $ Ln2 @ FUNC: ; 11 :{ ; 12: printf ("false/N "); Push offset $ sg3678 Call _ printf Add ESP, 4 $ Ln3 @ FUNC: ; 13 :} ; 14 :} Pop EBP RET 0 ?? $ Func @ $00 @ yaxxz endp; func <1> _ Text ends

Oh! The soft cl.exe still adds conditional judgment. Let's try again with the optimization options:
; Call E:/win2003_program/vs2005/VC/bin/vcvars32.bat
; Cl.exe/Fas main. CPP/O1

Public ?? _ C @ _ 05lfiobdml @ true? 6? $ Aa @; 'string' Public ?? $ Func @ $00 @ yaxxz; func <1> Extrn _ printf: Proc ; Comdat ?? _ C @ _ 05lfiobdml @ true? 6? $ Aa @ ; File F:/practice/C_c ++/2008-01-03/testtemplate/Main. cpp Const segment ?? _ C @ _ 05lfiobdml @ true? 6? $ Aa @ dB 'true', 0ah, 00 h; 'string' ; Function compile flags:/ogspy Const ends ; Comdat ?? $ Func @ $00 @ yaxxz _ Text Segment ?? $ Func @ $00 @ yaxxz proc; func <1>, comdat ; 6: If (value) ; 7 :{ ; 8: printf ("True/N "); Push offset ?? _ C @ _ 05lfiobdml @ true? 6? $ Aa @ Call _ printf Pop ECx ; 9 :} ; 10: else ; 11 :{ ; 12: printf ("false/N "); ; 13 :} ; 14 :} RET 0 ?? $ Func @ $00 @ yaxxz endp; func <1> _ Text ends

Well, good! After the optimization option is added, no conditions are determined.

To sum up, using templates for Conditional compilation can be more flexible without any impact on efficiency.

Another problem is that you must add func <true> or func <false> to each call. You do not know how to set a default parameter. I tried the template <bool value = true> and the result cannot be compiled. If you have any good solutions, please let me know. Thank you!