preprocessor-directive

问题 I tried making a quick macro for creating and showing a simple "ok" dialog box in iOS: #define ALERT_DIALOG(title,message) \ do\ {\ UIAlertView *alert_Dialog = [[UIAlertView alloc] initWithTitle:(title) message:(message) delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];\ [alert_Dialog show];\ } while ( 0 ) If I try to use it in my code: ALERT_DIALOG(@"Warning", @"Message"); I get the error: Parse Issue. Expected']' And the error seems to be pointing at the second @ right before

问题 I want to conditionally compile code in one VBAproject, with a condition that depends on some registry-entry. Is this somehow possible in VBA? I know that there are some simple preprocessing possibilites in VBA, but I can not see if it is possible to somehow access the registry while preprocessing. Or Maybe some other possibility to check the registry before compiling. Since I get a compile error because of some missing reference(and thus missing class object), I aim to check the registry

问题 I have a C code: ... void caller() { #define YES 1 #define NO 0 } ... Will the both #define lines execute when caller is called/executed, or will they execute at compile-time only. 回答1: The prerpcessor macros don't execute, they are just named fragments of the code which will be replaced by the preprocessor to theirs content if you use them. Read more about preprocessor macros here. So, after preprocessing, your code will be: void caller() { } Let assume you use the YES macro after you

问题 which global variable can be used in the preprocessor directive file.cpp int variable = 1; #if variable >= 1 int a = 0; #else int a = 1; #endif or file.cpp const int variable = 1; #if variable >= 1 int a = 0; #else int a = 1; #endif or file.cpp #include "header.h" // extern in variable; in the header.h #if variable >= 1 int a = 0; #else int a = 1; #endif What are the rules which governs using the variables in the proprocessor directive? If a variable which can be consant folded, can it be

问题 I have a set of arrays : msg1[] msg2[] .... msgn[] . And I need to use the values in a while loop. as msgi[] . When I define it as #define MSG(a) msg##a and put it in a loop and increment i , it expands it to msgi ? 回答1: You can't do it that way. Instead you could create a new array, that contains pointers to the actual arrays: int array1[...]; int array2[...]; int *all_arrays[] = { array1, array2 }; 回答2: build your c code with gcc -E myfile.c and you will see the reason this called

问题 Here's a concrete example of what I want to do. Consider the string.Join function. Pre-.NET 4.0, there were only two overloads, both of which required a string[] parameter. As of .NET 4.0, there are new overloads taking more flexible parameter types, including IEnumerable<string> . I have a library which includes a Join function that does essentially what the .NET 4.0 string.Join function does. I was just wondering if I could make this function's implementation dependent on the .NET framework

问题 #include <iostream> int main() { int value1 = 1, value2 = 10; std::cout << "Min = " << std::min(value1,value2) <<std::endl; std::cout << "Max = " << std::max(value1,value2)<< std::endl; } As far as I know, the min and max functions are defined in <algorithm> . If I didn't tell the pre-processor to include <algorithm> why does the code still work? 回答1: Most likely, something inside of iostream has directly or indirectly included some other header that defines std::min and std::max . (Perhaps

问题 What's the analog to #ifdef __IPHONE_8_0 for OS X 10.10? I've RTM/STFI, enough at least. 回答1: #ifdef __MAC_10_10 The #define s for the OS versions are in Availability.h . 来源： https://stackoverflow.com/questions/25554537/analog-to-iphone-8-0-for-os-x-10-10

问题 This question already has an answer here : Hint for lookup table set bit count algorithm (1 answer) Closed 6 years ago . static const unsigned char BitsSetTable256[256] = { # define B2(n) n, n+1, n+1, n+2 # define B4(n) B2(n), B2(n+1), B2(n+1), B2(n+2) # define B6(n) B4(n), B4(n+1), B4(n+1), B4(n+2) B6(0), B6(1), B6(1), B6(2) }; This code is very famous in set bit problem.. I have understand how it will output a lookup table at compile time. but I need more intuition for this .. means What is

问题 How to inject C# Preprocessor Directives to an interface by Reflection ? Example : I want to inject #if SILVERLIGHT to any WCF service contract interface. 回答1: Short answer: you can't. Slightly longer answer: you question doesn't even make sense in the first place. Preprocessor directives are processed before compilation. The result of that processing is the new, modified, source code. That source code then gets compiled. For example, if the SILVERLIGHT symbol is not defined at the time of