All Questions
162
questions
161
votes
2
answers
54k
views
Is #pragma once part of the C++11 standard?
Traditionally, the standard and portable way to avoid multiple header inclusions in C++ was/is to use the #ifndef - #define - #endifpre-compiler directives scheme also called macro-guard scheme (see ...
- 42.3k
141
votes
3
answers
74k
views
When should I prefer constexpr variables over macros?
Where should I prefer using macros and where should I prefer constexpr?
Aren't they basically the same?
#define MAX_HEIGHT 720
vs
constexpr unsigned int max_height = 720;
- 1,605
32
votes
2
answers
20k
views
Expand macro inside string literal
What I'm trying to do is to #define a macro:
#define a(2)
and later use it inside a string literal: string = "a";.
I want that string to be interpreted not as string but to get the value of a, i.e. ...
- 347
31
votes
3
answers
14k
views
Are empty macro arguments legal in C++11?
I sometimes deliberately omit macro arguments. For example, for a function-like macro like
#define MY_MACRO(A, B, C) ...
I might call it as:
MY_MACRO(, bar, baz)
There are still technically 3 ...
- 18.2k
28
votes
4
answers
2k
views
How to allow copy elision construction for C++ classes (not just POD C structs)
Consider the following code:
#include <iostream>
#include <type_traits>
struct A
{
A() {}
A(const A&) { std::cout << "Copy" << std::endl; }
A(A&&) { std::...
- 22.8k
24
votes
3
answers
4k
views
C++ macro '##' doesn't work after '->' operator
I have a shared_ptr object x, which has get and set methods as follows:
x->a_value();
x->set_a_value();
x->b_value();
x->set_b_value();
When i try to define a macro:
#define MAC(...
- 659
23
votes
1
answer
5k
views
Understanding DEFER and OBSTRUCT macros
I created a small macro metaprogramming library that implements basic useful constructs such as REPEAT(times, x), IF(value, true, false), tuples, and more.
Most of my implementations work by ...
- 91.7k
21
votes
1
answer
10k
views
PyBind11 Template Class of Many Types
I'd like to use PyBind11 to wrap a specialized array class. However, the array is available in many flavours (one per each plain-old-datatype). The code looks like this:
py::class_<Array2D<...
- 58.6k
21
votes
6
answers
18k
views
Display integer at compile time in static_assert()
Here is a simplified version of what I'm trying to do
enum First
{
a,
b,
c,
nbElementFirstEnum,
};
enum Second
{
a,
b,
c,
nbElementSecondEnum,
};
static_assert(
...
- 677
17
votes
3
answers
5k
views
C++11 nested macro invocation?
It says in C++ std 16.3.4:
The resulting preprocessing token sequence [from a macro invocation replacement]
is rescanned, along with all subsequent preprocessing tokens of the source file, for ...
- 67.2k
10
votes
3
answers
7k
views
What does the "__cplusplus" macro expand to?
What does the C++ macro __cplusplus contain and expand to?
Does the macro __cplusplus always, even in oldest C++ implementation, contain and expand to a numeric value?
Is it safe to use #if ...
- 8,208
10
votes
3
answers
4k
views
C++ or macro magic to generate method and forward arguments
I would like to create a magical macro, or anything, that would generate a something like this:
MAGICAL_MACRO(return_type, method_name, ...)
should work like this:
MAGICAL_MACRO(void, Foo, int a, ...
- 415
10
votes
1
answer
9k
views
How to single out the first parameter sent to a macro taking only a variadic parameter
I try to get at the first actual parameter sent to a variadic macro. This is what I tried, and which does not work in VS2010:
#define FIRST_ARG(N, ...) N
#define MY_MACRO(...) decltype(FIRST_ARG(...
- 527
7
votes
2
answers
10k
views
Getting too many arguments provided to function-like macro invocation compile error while defining lambda inside assert (assert.h) in Xcode [c++]
I am using assertion macro from assert.h
I have defined lambda to perform assertion checking.
int val1 = 0;
int val2 = 1;
const auto check = [val1,val2]()-> bool
{
return val1 < val2;
};
//...
- 3,255
7
votes
5
answers
3k
views
how to check if function exists
I want to implement my own std::make_unique function with the function being part of std namespace. I know this helper function is added to C++14 but I do not have it in C++11. So, I want to check it ...
- 7,775
7
votes
3
answers
247
views
Can Template / Preprocessor hackery be used to support variable arguments in the middle of an argument list?
I have stumbled upon old code that looks like this:
void dothing(bool testBool,
const std::string& testString1,
const std::string& file,
int line,
...
- 1,597
7
votes
2
answers
361
views
Is it possible to write a macro existenceof(S,f) or hasfield(S,f) in C++11?
I'm reasonably familiar with the standard metaprogramming solutions (e.g. C++11 ways of finding if a type has member function or supports operator?) which don't involve macro magic. However, I have a ...
- 24.8k
6
votes
3
answers
432
views
How can I create a macro which uses a value multiple times, without copying it?
I'd like to create a macro which unpacks a pair into two local variables. I'd like to not create a copy of the pair if it's just a variable, which this would accomplish:
#define UNPACK_PAIR(V1, V2, ...
- 227k
6
votes
3
answers
666
views
Find unexecuted lines of c++ code
As part of my unit testing I want to ensure code coverage of the tests. The aim is to place something like REQUIRE_TEST macros somewhere in the code and check whether all of these were called.
void ...
- 3,379
5
votes
4
answers
3k
views
Return from calling function inside lambda
Lambdas are an awesome way to create reusable code inside a function/method without polluting the parent class. They're a very functional replacement for C-style macros most of the time.
However, ...
- 3,791
5
votes
4
answers
865
views
macro for switching between auto_ptr and unique_ptr
In a project that still uses pre-C++11 I wanted to prepare the source for the switch by compiling with a C++11 compiler and fixing the errors. They consisted of
instances of std::auto_ptr<T> ...
- 2,585
5
votes
4
answers
3k
views
single expression helper for compile-time enforced constexpr function evaluation possible?
@cyberpunk_ is trying to achieve something and made some questions about it but all the chase boils down to this:
Is it possible to build a tool to enforce compile-time evaluation of a constexpr ...
- 11.7k
5
votes
4
answers
3k
views
Custom `assert` macro that supports commas and error message
I would like to create a custom version of the assert macro defined in <cassert>, that displays an error message when the assertion fails.
Desired usage:
custom_assert(AClass<T1, T2>::...
- 91.7k
4
votes
6
answers
7k
views
How to use #ifndef with macro argument?
I have a simple code in header.h-
#define SWAP(a, b) {a ^= b; b ^= a; a ^= b;}
This header.h is included in a code.c file, but my requirement is-
I want SWAP to be checked first like-
#ifndef ...
- 77
4
votes
3
answers
428
views
Getting rid of an ugly C construct
I have inherited a (large) piece of code which has an error tracking mechanism where they pass in a boolean variable to all the methods they call and on errors at various stages of execution the ...
- 34.8k
4
votes
2
answers
4k
views
Change a string macro at compilation time
I'm developing an unique client that has to work on different machines. In every machine the server is running in a different IP address, but this address is known.
I don't want to tell the client ...
- 115
4
votes
2
answers
300
views
Macro compiles with GCC but not with VS11
I have written the following code to assist restricting my template functions to certain types, with meaningful error message when other types were used. I had the idea from a different question in ...
- 118
4
votes
3
answers
5k
views
How to extract __VA_ARGS__?
I hava a macro to call static function for each args.
For example:
#define FOO(X) X::do();
#define FOO_1(X,Y) X::do(); Y::do();
My question is that I need to use foo with variable number of ...
- 541
4
votes
1
answer
235
views
C+11-Like Type Decay in Rust
In C++11, you can decay a generic type to a value type, removing reference/rvalue semantics and cv-qualifiers, e.g.
decay<int>::type // type is `int`
decay<const int&>::type // type ...
- 295
4
votes
2
answers
2k
views
Is there a cross platform way to detect debug mode compilation?
Is there a cross platform way to detect debug mode compilation? If not, then how to do it for the top compilers; MSVC, GNU & MINGW, mac, clang, intel.
For example MSVC you can detect debug mode ...
- 5,163
4
votes
2
answers
1k
views
Is it possible to detect namespace membership in C++?
For C++ types, the <type_traits> header gives us many useful compile-time reflection capabilities. E.g. std::is_base_of<B, D>::value determines at compile-time whether B is a base class of ...
- 69.9k
4
votes
2
answers
1k
views
C++ macro to test availability of __func__, __FUNCTION__, __PRETTY_FUNCTION__, etc
Various modern C/C++ compilers include one or both of __func__ / __FUNCTION__ for purposes of logging the currently executing function. MSVC++ also includes __FUNCSIG__ and GCC __PRETTY_FUNCTION__ as ...
- 191
4
votes
1
answer
331
views
instantiating template functions and classes with boost preprocess
Working with the seemingly standard w, x, y, z demos, suppose I have the following macro trying to be converted to an "iterable" preprocessor macro
#define INSTANTIATE_FUNC(rtype, func_name, ...) \
...
- 843
3
votes
3
answers
645
views
"Beautifying" macro
Watching Herb Sutter's talk about atomics at C++ and beyond I glimpsed at his idea of an easy to use lock/unlock mechanism that may or may not come in a future standard of the language.
The mechanism ...
- 1,480
3
votes
2
answers
165
views
Need explanation over the behavior of C++ code
I need a little explanation over how this C++ code is behaving and returning value
#include<iostream>
using namespace std;
#define MY_MACRO(n) #n
#define SQR(x) x * x
int main()
{
//cout<...
- 2,442
3
votes
3
answers
2k
views
Variadic macros
Is there any way to write a macro like this:
#define G(x1, x2, ... , xn) f(x1), f(x2), ... , f(xn)
Or do I need to define this for each individual n?
C++0x answers are ok.
Edit: I'm asking how to ...
- 22.8k
3
votes
2
answers
1k
views
What's the difference between the noexcept keyword and _NOEXCEPT macro?
I'm a beginner to C++ and I'm learning about some of the C++11 features. One thing I noticed was that in some parts of the Visual C++ stdlib, the authors used the _NOEXCEPT macro instead of the ...
- 33.4k
3
votes
2
answers
494
views
Any clean way to get OpenMP pragmas to work with macros?
I have to add OpenMP to a customer's code. It has a couple of macros that work sort of like so:
int i, imax;
#ifdef MAC1
double x1, y1
#endif
#ifdef MAC2
double x2, y2
#endif
//first loop:
for (i=0;...
- 6,405
3
votes
3
answers
267
views
Is there a macro or provision to check is the line of code is inside a class?
I have a c style macro in my code, which prints the logs. I want to alter the macro to print the this pointer. But, there are some portion of a code, which is not a member function of a class or some ...
- 1,934
3
votes
1
answer
221
views
Throwing function-like variadic macro wrapping, replacing thrown exception
Suppose I have a third party library that provides a function-like ThirdPartyMacro macro that is:
Variadic and accepts arbitrary tokens, not just well formed c++ expressions. After parsing the ...
- 12.9k
3
votes
2
answers
5k
views
Replace characters in preprocessor definition
I have a definition which includes a path (with no escape sequence) like this one:
// Incorrect
#define PATH "c:\blah\blah\file.cfg"
I would rather like it as this:
// Corrected
#define PATH "c:\\...
- 10.7k
3
votes
2
answers
630
views
In C++, static assert that a declaration at current position would not be enclosed in any namespace?
In C++ one sometimes has annoying bugs where someone forgot to close out a namespace which was opened in a header file, and it can sometimes be difficult to track down exactly which one.
Somewhat ...
- 15.9k
3
votes
4
answers
160
views
Defining macro improving syntax of specific function
I've created a function declared as:
template <typename Container, typename Task>
void parallel_for_each(Container &container, Task task,
unsigned number_of_threads = ...
- 918
3
votes
2
answers
2k
views
Expanding macro inside raw string
I would like to do some debugging of my crazy macros, but there's no way to do it because macros generate code, not strings. I'd have to change the macros to emit strings in order for my program to ...
- 42.3k
3
votes
2
answers
145
views
Is there some way to determine whether the context allows the use of "this"?
Is there some way to determine whether the context allows the use of "this"?
My goal is write a generic macro, for logging, which depending on the context use "this" (for instance, for print the ...
- 177
3
votes
2
answers
402
views
How to detect if VS C++ compiler supports C++11?
How to detect if Visual Studio (VS) C++ compiler supports C++11 through preprocessor macros? I tried with __cplusplus (the preprocessor macro that many people advise to use for this kind of checks) ...
user7698505
3
votes
1
answer
154
views
Get subsets of macro values using offset
I have a list defined as a preprocessor value #define LIST 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. I want to write a macro that gets an index 0 or 1 and evaluates to a subset of the LIST such that for index 0 ...
- 3,889
3
votes
1
answer
977
views
Compiler macro to test difference between uint64_t and unsigned long long int
I have C++11 code that is failing to compile because an overloaded function is redefined with the same types as arguments:
char const* foo(uint64_t) { return "%" PRIu64; }
char const* foo(unsigned ...
- 96.7k
3
votes
2
answers
595
views
Checking for availability of C++0x algorithm additions
I'm trying to figure out which of the additions to the algorithm headers are supported by a given implementation (gcc and MSVC would be enough).
The simple way would be to do it the same way as one ...
- 59.3k
3
votes
0
answers
521
views
Function argument as __builtin_constant_p?
Is it possible to have a function argument which is __builtin_constant_p?
This macro works fine:
#define FOO(a) {\
static_assert(__builtin_constant_p(a));\
}
void bar() {
FOO("abc");
}
I ...
- 9,787