All Questions
Tagged with macros c-preprocessor
1,329
questions
249
votes
10
answers
100k
views
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'...
- 67.2k
198
votes
15
answers
185k
views
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
152
votes
11
answers
80k
views
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
131
votes
8
answers
59k
views
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
129k
views
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
123
votes
24
answers
134k
views
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
45k
views
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 ...
- 10.7k
101
votes
7
answers
81k
views
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
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 ...
- 37.1k
92
votes
8
answers
36k
views
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?
- 11.1k
83
votes
18
answers
41k
views
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 ...
- 8,436
82
votes
9
answers
178k
views
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
81
votes
6
answers
68k
views
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 ...
- 1,059
81
votes
3
answers
3k
views
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 ...
- 1,644
80
votes
5
answers
48k
views
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 ...
- 831
78
votes
10
answers
21k
views
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
66
votes
6
answers
59k
views
How to undefine a define at commandline using GCC
How do I at compile time undefine a compiler macro using GCC? I tried some compile arguments to GCC, like -D, but I can't get to see the "not defined" message.
#include <iostream>
#...
- 6,820
65
votes
4
answers
3k
views
Why is this macro replaced as 20 instead 10?
1. #define NUM 10
2. #define FOO NUM
3. #undef NUM
4. #define NUM 20
5.
6. FOO
When I only run the preprocessor, the output file contains 20.
However, from what I understand, the preprocessor ...
- 11.7k
65
votes
3
answers
2k
views
In a GNU C macro envSet(name), what does (void) "" name mean?
I came across this syntax today and couldn't work out what it meant:
// Uses the GNU C statement expression extension
#define envSet(name) ({ \
static int initialised; \
static bool set; \
(void) "" ...
- 8,075
62
votes
5
answers
91k
views
Which Cross Platform Preprocessor Defines? (__WIN32__ or __WIN32 or WIN32 )?
I often see __WIN32, WIN32 or __WIN32__. I assume that this depends on the used preprocessor (either one from visual studio, or gcc etc).
Do I now have to check first for os and then for the used ...
- 8,652
59
votes
4
answers
33k
views
What does #x inside a C macro mean?
For example I have a macro:
#define PRINT(int) printf(#int "%d\n",int)
I kinda know what is the result.
But how come #int repersent the whole thing?
I kinda forget this detail. Can anybody kindely ...
- 4,690
54
votes
2
answers
52k
views
error: pasting "." and "red" does not give a valid preprocessing token
I'm implementing The X macro, but I have a problem with a simple macro expansion. This macro (see below) is used into several macros usage examples, by including in this article.
The compiler gives ...
- 16.5k
52
votes
11
answers
31k
views
Why aren't there macros in C#?
When learning C# for the first time, I was astonished that they had no support for macros in the same capacity that exists in C/C++. I realize that the #define keyword exists in C#, but it is greatly ...
- 6,987
51
votes
8
answers
48k
views
How to generate a newline in a cpp macro?
How do I write a cpp macro which expands to include newlines?
- 511
49
votes
7
answers
25k
views
Variadic recursive preprocessor macros - is it possible?
I've run into a little theoretical problem. In a piece of code I'm maintaining there's a set of macros like
#define MAX_OF_2(a, b) (a) > (b) ? (a) : (b)
#define MAX_OF_3(a, b, c) MAX_OF_2(...
- 12.8k
49
votes
3
answers
12k
views
Opposite of C preprocessor "stringification"
When using C preprocessor one can stringify macro argument like this:
#define TO_STRING(x) "a string with " #x
and so when used, the result is as follows:
TO_STRING(test) will expand to: "a string ...
- 1,183
48
votes
5
answers
143k
views
Error: macro names must be identifiers using #ifdef 0
I have the source code of an application written in C++ and I just want to comment something using:
#ifdef 0
...
#endif
And I get this error
error: macro names must be identifiers
Why is this ...
- 20.5k
47
votes
8
answers
45k
views
Escaping a # symbol in a #define macro?
Without going into the gory details I want to use a #define macro that will expand to a #include but the '#' sign is confusing the preprocessor (as it thinks I want to quote an argument.)
For example,...
- 77.5k
47
votes
3
answers
15k
views
Can I redefine a C++ macro then define it back?
I am using both the JUCE Library and a number of Boost headers in my code. Juce defines "T" as a macro (groan), and Boost often uses "T" in it's template definitions. The result is that if you ...
- 1,968
44
votes
2
answers
57k
views
What's the difference between #if and #ifdef Objective-C preprocessor macro?
How to define preprocessor macros in build settings, like IPAD_BUILD, and IPHONE_BUILD (and how to use them in my factory methods)?
I'm using these by heart now, would be cool to know what is going ...
- 16.2k
43
votes
2
answers
54k
views
Expand macros inside quoted string [duplicate]
Possible Duplicate:
C Macros to create strings
I have a function which accepts one argument of type char*, like f("string");
If the string argument is defined by-the-fly in the function call, ...
- 2,142
43
votes
9
answers
56k
views
macro definition containing #include directive
Is there a way to define a macro that contains a #include
directive in its body?
If I just put
the "#include", it gives the error
C2162: "expected macro formal parameter"
since here I am not using #...
- 1,024
41
votes
8
answers
43k
views
The need for parentheses in macros in C [duplicate]
I tried to play with the definition of the macro SQR in the following code:
#define SQR(x) (x*x)
int main()
{
int a, b=3;
a = SQR(b+5); // Ideally should be replaced with (3+5*5+3), ...
- 3,130
39
votes
6
answers
72k
views
Is there a way to both check a macro is defined and it equals a certain value at the same time
I regularly use object-like preprocessor macros as boolean flags in C code to turn on and off sections of code.
For example
#define DEBUG_PRINT 1
And then use it like
#if(DEBUG_PRINT == 1)
...
- 1,801
38
votes
3
answers
11k
views
What is the difference between a preprocessor macro with no arguments, and one with zero arguments
Is there any reason to prefer
#define MY_MACRO() ..stuff..
to
#define MY_MACRO ..stuff..
Don't use macros is not a valid answer...
- 2,082
33
votes
7
answers
30k
views
Macros to create strings in C
Alternative titles (to aid search)
Convert a preprocessor token to a string
How can I make a char string from a C macro's value?
Original Question
I would like to use C #define to build literal ...
- 25.7k
32
votes
18
answers
19k
views
The most useful user-made C-macros (in GCC, also C99)? [closed]
What C macro is in your opinion is the most useful? I have found the following one, which I use to do vector arithmetic in C:
#define v3_op_v3(x, op, y, z) {z[0]=x[0] op y[0]; \
...
- 29.9k
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
32
votes
4
answers
10k
views
Why is this C or C++ macro not expanded by the preprocessor?
Can someone points me the problem in the code when compiled with gcc 4.1.0.
#define X 10
int main()
{
double a = 1e-X;
return 0;
}
I am getting error:Exponent has no digits.
When I replace X ...
- 1,126
32
votes
7
answers
40k
views
Is it possible for C preprocessor macros to contain preprocessor directives?
I would like to do the equivalent of the following:
#define print_max(TYPE) \
# ifdef TYPE##_MAX \
printf("%lld\n", TYPE##_MAX); \
# endif
print_max(INT);
Now the #ifdef or any nested ...
- 31.1k
30
votes
8
answers
109k
views
Is it possible to use a if statement inside #define?
I'm trying to make a macro with the following formula: (a^2/(a+b))*b, and I want to make sure that the there will be no dividing by zero.
#define SUM_A( x, y ) if( x == 0 || y == 0) { 0 } else { ( ( ...
- 433
30
votes
1
answer
10k
views
GCC define function-like macros using -D argument
Problem
I am trying to remove __attribute__ from my C code before I send it into a parser. Is there a way to define function-like macros using the -D argument?
Solution using header file
#define ...
- 6,762
29
votes
5
answers
31k
views
Determine #defined string length at compile time
I have a C-program (an Apache module, i.e. the program runs often), which is going to write() a 0-terminated string over a socket, so I need to know its length.
The string is #defined as:
#define ...
- 22.4k
29
votes
5
answers
26k
views
Is #if defined MACRO equivalent to #ifdef MACRO?
I have code that I want to have two modes, debug and verbose. I define them in my header file as,
#define verbose TRUE
#define debug TRUE
In my code so far, I have just been using
#if(debug)
//code
...
- 33.9k
28
votes
8
answers
39k
views
Creating a string list and an enum list from a C++ macro
In order to make my code shorter and easier to change I want to replace something like
enum{ E_AAA, E_BBB, E_CCC };
static const char *strings{"AAA", "BBB", "CCC" };
With a macro, like INIT(AAA, BBB,...
- 271
27
votes
3
answers
41k
views
What exactly do C include guards do?
Let's say I have a header file "header.h" with a function definition.
#ifndef HEADER_FILE
#define HEADER_FILE
int two(void){
return 2;
}
#endif
This header file has an include guard. ...
- 4,649
26
votes
13
answers
14k
views
Can I determine if an argument is string literal?
Is it possible to determine if an argument passed in macro or function is a string literal at compile time or run time?
For example,
#define is_string_literal(X)
...
...
is_string_literal("...
- 301
26
votes
3
answers
13k
views
Macro evaluation order [duplicate]
Possible Duplicate:
# and ## in macros
why the output of second printf is f(1,2) what is the order in which macro is evaluated?
#include <stdio.h>
#define f(a,b) a##b
#define g(a) #a
#...
- 3,147
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
24
votes
2
answers
13k
views
Difference between #pragma and _Pragma() in C
What is the difference between #pragma and _Pragma() in C?
syntax:
#pragma arg
and
_Pragma(arg)
When should I use _Pragma(arg)?
- 4,863