Questions tagged [macros]
***DO NOT USE for VBA / MS-Office languages. Use [vba] instead.*** A macro is a rule or pattern that specifies how a certain input sequence (often a sequence of characters) should be mapped to an output sequence (also often a sequence of characters) according to a defined procedure.
macros
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What is ':-!!' in C?
I bumped into this strange macro code in /usr/include/linux/kernel.h:
/* Force a compilation error if condition is true, but also produce a
result (of value 0 and type size_t), so the expression ...
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360
votes
15
answers
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views
What makes Lisp macros so special?
Reading Paul Graham's essays on programming languages one would think that Lisp macros are the only way to go. As a busy developer, working on other platforms, I have not had the privilege of using ...
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306
votes
6
answers
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Strange definitions of TRUE and FALSE macros
I have seen the following macro definitions in a coding book.
#define TRUE '/'/'/'
#define FALSE '-'-'-'
There was no explanation there.
Please explain to me how these will work as TRUE and FALSE.
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2
answers
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how to use #ifdef with an OR condition?
Sorry for asking very basic question. I would like to set OR condition in #ifdef directive.?
How to do that ?
I tried
#ifdef LINUX | ANDROID
...
..
#endif
It did not work? What is the proper way?
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10
answers
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Overloading Macro on Number of Arguments
I have two macros FOO2 and FOO3:
#define FOO2(x,y) ...
#define FOO3(x,y,z) ...
I want to define a new macro FOO as follows:
#define FOO(x,y) FOO2(x,y)
#define FOO(x,y,z) FOO3(x,y,z)
But this doesn'...
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231
votes
1
answer
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C multi-line macro: do/while(0) vs scope block [duplicate]
Possible Duplicates:
What’s the use of do while(0) when we define a macro?
Why are there sometimes meaningless do/while and if/else statements in C/C++ macros?
do { … } while (0) ...
- 3,055
219
votes
31
answers
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__FILE__ macro shows full path
The standard predefined macro __FILE__ available in C shows the full path to the file. Is there any way to shorten the path and get just the filename? I mean instead of
/full/path/to/file.c
I see
to/...
- 23.9k
213
votes
6
answers
63k
views
Saving vim macros
Does anyone know how to properly save/reuse macros recorded inside of a vim editor?
- 3,574
205
votes
10
answers
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Can I record/play macros in Visual Studio 2012/2013/2015/2017/2019?
Apparently macros were dropped from Visual Studio 2012.
Is there a plugin/extension/tool that will let me record & play keyboard macros (much like the record/play temporary macro in ...
- 58.5k
198
votes
15
answers
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How do I show the value of a #define at compile-time?
I am trying to figure out what version of Boost my code thinks it's using. I want to do something like this:
#error BOOST_VERSION
but the preprocessor does not expand BOOST_VERSION.
I know I could ...
- 14.7k
195
votes
5
answers
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views
What does "#pragma comment" mean?
What does #pragma comment mean in the following?
#pragma comment(lib, "kernel32")
#pragma comment(lib, "user32")
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181
votes
1
answer
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Getting a structural type with an anonymous class's methods from a macro
Suppose we want to write a macro that defines an anonymous class with some type members or methods, and then creates an instance of that class that's statically typed as a structural type with those ...
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176
votes
70
answers
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What is the worst real-world macros/pre-processor abuse you've ever come across?
What is the worst real-world macros/pre-processor abuse you've ever come across (please no contrived IOCCC answers *haha*)?
Please add a short snippet or story if it is really entertaining. The goal ...
161
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2
answers
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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
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votes
6
answers
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What does the Q_OBJECT macro do? Why do all Qt objects need this macro?
I just started using Qt and noticed that all the example class definitions have the macro Q_OBJECT as the first line. What is the purpose of this preprocessor macro?
- 18.8k
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11
answers
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Are typedef and #define the same in C?
I wonder if typedef and #define are the same in C. What are the differences between them?
user188276
145
votes
8
answers
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Where are the recorded macros stored in Notepad++?
I have recorded a macro that I want to share with my work colleague.
In what location are these recorded macros saved, so that I can add it to his machine?
If interested, the macro is for taking a ...
- 3,121
144
votes
2
answers
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What's the use of do while(0) when we define a macro? [duplicate]
Possible Duplicates:
Do-While and if-else statements in C/C++ macros
do { … } while (0) — what is it good for?
I'm reading the linux kernel and I found many macros like this:
#define ...
- 4,577
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votes
6
answers
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How can I pass a macro definition from "make" command line arguments (-D) to C source code?
I usually pass macro definitions from "make command line" to a "makefile" using the option:
-Dname=value. The definition is accessible inside the makefile.
I also pass macro ...
- 2,880
141
votes
3
answers
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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
140
votes
16
answers
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Optional Parameters with C++ Macros
Is there some way of getting optional parameters with C++ Macros? Some sort of overloading would be nice too.
- 11.5k
139
votes
16
answers
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Is there a __CLASS__ macro in C++?
Is there a __CLASS__ macro in C++ which gives the class name similar to __FUNCTION__ macro which gives the function name
- 1,393
137
votes
14
answers
91k
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Inline functions vs Preprocessor macros
How does an inline function differ from a preprocessor macro?
- 1,403
131
votes
8
answers
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Comma in C/C++ macro
Say we have a macro like this
#define FOO(type,name) type name
Which we could use like
FOO(int, int_var);
But not always as simply as that:
FOO(std::map<int, int>, map_var); // error: ...
- 2,115
129
votes
4
answers
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How to identify platform/compiler from preprocessor macros?
I'm writing a cross-platform code, which should compile at linux, windows, Mac OS. On windows, I must support visual studio and mingw.
There are some pieces of platform-specific code, which I should ...
- 4,187
128
votes
4
answers
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Swift: how to use PREPROCESSOR Flags (like `#if DEBUG`) to implement API keys?
In Objective-C it was sometimes useful to use static string constants to define alternate API keys (for example to differentiate between RELEASE and DEBUG keys for analytics packages, like MixPanel, ...
- 5,544
128
votes
2
answers
74k
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Creating C macro with ## and __LINE__ (token concatenation with positioning macro)
I want to create a C macro that creates a function with a name based
on the line number.
I thought I could do something like (the real function would have statements within the braces):
#define UNIQUE ...
- 1,283
127
votes
4
answers
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Jinja2 inline comments
How can I put comments inside Jinja2 argument list declaration ?
Everything I have tried gives an error:
jinja2.exceptions.TemplateSyntaxError: unexpected char u'#'
{{ Switch('var',
[('1', 'foo')...
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votes
24
answers
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Macro definition to determine big endian or little endian machine?
Is there a one line macro definition to determine the endianness of the machine? I am using the following code but converting it to macro would be too long:
unsigned char test_endian( void )
{
int ...
- 11.2k
121
votes
3
answers
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What predefined macro can I use to detect clang?
I'm trying to detect the compiler used to compile my source code. I can easily find predefined macros to check for MSVC or GCC (see https://github.com/cpredef/predef for example), but I cannot find ...
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votes
10
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How can I convert from degrees to radians?
I am trying to convert this Obj-C code to Swift code but I don't know what the equivalent of this code should be ?
#define DEGREES_TO_RADIANS(degrees)((M_PI * degrees)/180)
I googled and found this
...
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votes
9
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Is there a macro recorder for Eclipse? [closed]
Is there a good Eclipse plugin for recording and playing back macros?
I've tried this one, but it didn't do me any good- it seemed like it wasn't ready for prime time.
I know about editor templates, ...
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13
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iOS How to detect iPhone X, iPhone 6 plus, iPhone 6, iPhone 5, iPhone 4 by macro?
How to detect device model by macro?
i had using something like this but the result on the simulator alway IS_IPHONE_5
#define IS_IPAD (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
#define ...
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votes
5
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replay a vim macro until end of buffer
I want to run a macro I just recorded in register "x" on every single line of an open buffer, from my cursor to end of the buffer, in vim. How do I do that?
I know I can replay the macro n ...
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votes
9
answers
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views
How can I define a string literal on the GCC command line?
On the GCC command line, I want to define a string such as -Dname=Mary. Then in the source code, I want printf("%s", name); to print Mary.
How could I do it?
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How to view C preprocessor output?
How do I view the output produced by the C pre-processor, prior to its conversion into an object file?
I want to see what the MACRO definitions do to my code.
user191776
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votes
3
answers
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Vim Macro on Every Line of Visual Selection
I'd like to run a macro on every line in a selection, rather than totalling up the number of lines in my head. For instance, I might write a macro to transform:
Last, First
Into
First Last
and I'd ...
- 23.7k
97
votes
7
answers
7k
views
Why only define a macro if it's not already defined?
All across our C code base, I see every macro defined the following way:
#ifndef BEEPTRIM_PITCH_RATE_DEGPS
#define BEEPTRIM_PITCH_RATE_DEGPS 0.2f
#endif
#ifndef ...
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votes
8
answers
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Real-world use of X-Macros
I just learned of X-Macros. What real-world uses of X-Macros have you seen? When are they the right tool for the job?
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What's the significance of a C function declaration in parentheses apparently forever calling itself?
In gatomic.c of glib there are several function declarations that look like this:
gboolean
(g_atomic_int_compare_and_exchange_full) (gint *atomic,
gint ...
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What is PRIu64 in C?
I am new to C and I am confronted with:
#include <stdio.h>
#include <inttypes.h>
int main(void)
{
uint64_t foo = 10;
printf("foo is equal to %" PRIu64 "!\n", ...
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18
answers
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What are C macros useful for?
I have written a little bit of C, and I can read it well enough to get a general idea of what it is doing, but every time I have encountered a macro it has thrown me completely. I end up having to ...
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C# Macro definitions in Preprocessor
Is C# able to define macros as is done in the C programming language with pre-processor statements? I would like to simplify regular typing of certain repeating statements such as the following:
...
cl123
82
votes
2
answers
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What's the point of a PROTOTYPE macro that merely expands to its arguments?
I have a header file which contains
#define PROTOTYPE(s) s
What is the point of that? Seems like it would just replace the input with itself.
There are TONS of other directives around it, but the ...
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votes
6
answers
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Can we have recursive macros?
I want to know if we can have recursive macros in C/C++? If yes, please provide a sample example.
Second thing: why am I not able to execute the below code? What is the mistake I am doing? Is it ...
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3
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Understanding the behavior of C's preprocessor when a macro indirectly expands itself
While I was working on a big project full of macro tricks and wizardry, I stumbled upon a bug in which a macro was not expanding properly. The resulting output was "EXPAND(0)", but EXPAND ...
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5
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Any utility to test expand C/C++ #define macros?
It seems I often spend way too much time trying to get a #define macro to do exactly what i want. I'll post my current dilemma below and any help is appreciated. But really the bigger question is ...
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3
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What are the implications of the linux __user macro?
I was hoping someone could explain the nuances of the __user macro used in the linux kernel source.
First of all, the macro:
# define __user __attribute__((noderef, address_space(1)))
Now, ...
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votes
3
answers
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How to allow optional trailing commas in macros?
Here's a synthetic example of what I want:
macro_rules! define_enum {
($Name:ident { $($Variant:ident),* }) => {
pub enum $Name {
None,
$($Variant),*,
}
...
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78
votes
10
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21k
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Array-size macro that rejects pointers
The standard array-size macro that is often taught is
#define ARRAYSIZE(arr) (sizeof(arr) / sizeof(arr[0]))
or some equivalent formation. However, this kind of thing silently succeeds when a pointer ...
- 174k