How do I make Xcode consider the values of my defines? - c

Question

How can I make Xcode consider the values of my defines to fold my code properly? Xcode seems to consider some things that aren't compile as part of the code -- with causes some issues for me :(
Example:
#include <stdio.h>
#define LIE_TO_THE_USER 1
void foobar(int argc)
{ // A
#if LIE_TO_THE_USER
if (0) { // B
#else
if (argc > 0) { // C
#endif
printf("argc is greater than 0\n");
} // D
else
{ // E
printf("argc is not greater than 0\n");
} // F
} // G
int main(int argc, const char * argv[])
{
foobar(argc);
return 0;
}
This code compiles... but is a pain to work with.
As far as Xcode is concerned, it folds brackets C and D together, E and F together, and folds C and G together (instead of folding A and G). Additionally, anything declared after the #if #else #endif (so just the main is this case) doesn't show up in this case.
In Visual Studio, it would just grey out the if (argc> 0 ) { // C and ignore it. But Xcode seems to consider it part of the code. I have found 2 workarounds:
void foobar(int argc)
{
#if LIE_TO_THE_USER
if (0)
#else
if (argc > 0)
#endif
{
printf("argc is greater than 0\n");
}
else
{
printf("argc is not greater than 0\n");
}
}
/// OR
void foobar(int argc)
{
#if LIE_TO_THE_USER
if (0) {
#else
if (argc > 0) {
#endif
printf("argc is greater than 0\n");
}
else
{
printf("argc is not greater than 0\n");
}
#if 0
}
#endif
}
However, this problem is veeeeery frequent in my project. So I would like to find to solve this problem automatically without having to worry about adding workarounds. Does anyone know a way to configure Xcode to ignore lines such as if (argc > 0) {?
Thanks in advance :)

Answer 1

This is one of the reasons macros are horrible; You can arbitrarily mess with the token stream and aren't bound to respect the language's structure.
Visual Studio is just completely ignoring whatever is eaten by the preprocessor, which means it reliably understands the structure of the code under the current defines but has no understanding of the code that's disabled. Xcode is trying to be smarter and to understand the entire program, but this works poorly when you use macros that really subvert the language's structure.
C++ is already hard enough for tools to work with, and the fundamental nature of the preprocessor makes it worse by essentially making it so that the same C++ source can produce arbitrarily many programs. You can avoid this problem by minimizing use of the preprocessor, and restricting uses to the simplest and most conventional, so that tools are likely to understand them.
In this case I think I would go with something like:
void foobar(int argc)
{
static constexpr bool tell_the_truth = false;
if (tell_the_truth && argc > 0)
{
printf("argc is greater than 0\n");
}
else
{
printf("argc is not greater than 0\n");
}
}
Or if you want to be able to configure this from the compilation command you can use:
static constexpr bool tell_the_truth = !LIE_TO_THE_USER
So that you can use a flag such as -DLIE_TO_THE_USER=true or -DLIE_TO_THE_USER=false.
The benefit of this approach is that tools' understanding of this program, the AST, actually represents the intended program and doesn't fundamentally change between configurations.

Answer 2

You can reduce the amount of code that looks like conditional compilation to Xcode by using a conditionally compiled macro, like this:
#define LIE_TO_THE_USER 1
...
#if LIE_TO_THE_USER
#define CONDITIONAL_LIE(A,B) (A)
#else
#define CONDITIONAL_LIE(A,B) (B)
#endif
With this macro in hand, you can rewrite your if as follows:
if (CONDITIONAL_LIE(0, argc > 0))
{
printf("argc is greater than 0\n");
}
else
{
printf("argc is not greater than 0\n");
}
The code would conditionally compile into the same output, but Xcode would think it's a regular if. This also looks cleaner to the reader.