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英文:

Recursion in Macro Preprocessor

问题

I am trying to write a function that calculates Factorial RECURSIVELY but I have problem with compiling the code. BTW, I do not know if the code itself is coorect!
The code:

#include <stdio.h>

#define FACTORIAL(n) \
    FACTORIAL_##n()

#define FACTORIAL_0() 0

#define FACTORIAL_1() 1

#define FACTORIAl_N(n) \
    FACTORIAL(n - 1) + FACTORIAL(n - 2)

#define FACTORIAL_RESULT(n) \
    FACTORIAL(n)

int main() {
    int f2 = FACTORIAL_RESULT(2);
    printf("%d\n", f2);
    return 0;
}

I get a bunch of errors when compiling this code such as:

*  Executing task: C:\MinGW\bin\gcc.exe c.c -o d:\C\output\c.exe -Wall -Wextra -g3 

 *  Terminal will be reused by tasks, press any key to close it. 

 *  Executing task: C:\MinGW\bin\gcc.exe c.c -o d:\C\output\c.exe -Wall -Wextra -g3 

c.c: In function 'main':
c.c:4:5: warning: implicit declaration of function 'FACTORIAL_2'; did you mean 'FACTORIAL_0'? [-Wimplicit-function-declaration]
    4 |     FACTORIAL_##n()
      |     ^~~~~~~~~~
c.c:14:5: note: in expansion of macro 'FACTORIAL'
   14 |     FACTORIAL(n)
      |     ^~~~~~~~~
c.c:17:14: note: in expansion of macro 'FACTORIAL_RESULT'
   17 |     int f2 = FACTORIAL_RESULT(2);
          |              ^~~~~~~~~~~~~~~~
c:/mingw/bin/../lib/gcc/x86_64-w64-mingw32/11.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: C:\Users\user1\AppData\Local\Temp\ccuGFhBc.o: in function `main':
D:\C/c.c:17: undefined reference to `FACTORIAL_2'
collect2.exe: error: ld returned 1 exit status

 *  The terminal process "C:\MinGW\bin\gcc.exe 'c.c', '-o', 'd:\C\output\c.exe', '-Wall', '-Wextra', '-g3'" terminated with exit code: 1. 
 *  Terminal will be reused by tasks, press any key to close it.

Anyone who can help me? Thanks in advance!

英文:

I am trying to write a function that calculates Factorial RECURSIVELY but I have problem with compiling the code. BTW, I do not know if the code itself is coorect!
The code:

#include <stdio.h>

#define FACTORIAL(n) \
    FACTORIAL_##n()

#define FACTORIAL_0() 0

#define FACTORIAL_1() 1

#define FACTORIAl_N(n) \
    FACTORIAL(n - 1) + FACTORIAL(n - 2)

#define FACTORIAL_RESULT(n) \
    FACTORIAL(n)

int main() {
    int f2 = FACTORIAL_RESULT(2);
    printf("%d\n", f2);
    return 0;
}

I get a bunch of errors when compiling this code such as:

*  Executing task: C:\MinGW\bin\gcc.exe c.c -o d:\C\output\c.exe -Wall -Wextra -g3 

 *  Terminal will be reused by tasks, press any key to close it. 

 *  Executing task: C:\MinGW\bin\gcc.exe c.c -o d:\C\output\c.exe -Wall -Wextra -g3 

c.c: In function 'main':
c.c:4:5: warning: implicit declaration of function 'FACTORIAL_2'; did you mean 'FACTORIAL_0'? [-Wimplicit-function-declaration]
    4 |     FACTORIAL_##n()
      |     ^~~~~~~~~~
c.c:14:5: note: in expansion of macro 'FACTORIAL'
   14 |     FACTORIAL(n)
      |     ^~~~~~~~~
c.c:17:14: note: in expansion of macro 'FACTORIAL_RESULT'
   17 |     int f2 = FACTORIAL_RESULT(2);
          |              ^~~~~~~~~~~~~~~~
c:/mingw/bin/../lib/gcc/x86_64-w64-mingw32/11.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: C:\Users\user1\AppData\Local\Temp\ccuGFhBc.o: in function `main':
D:\C/c.c:17: undefined reference to `FACTORIAL_2'
collect2.exe: error: ld returned 1 exit status

 *  The terminal process "C:\MinGW\bin\gcc.exe 'c.c', '-o', 'd:\C\output\c.exe', '-Wall', '-Wextra', '-g3'" terminated with exit code: 1. 
 *  Terminal will be reused by tasks, press any key to close it.

Anyone who can help me? Thanks in advance!

答案1

得分: 2

C标准不指定宏的动态创建。 #define FACTORIAL_N(n) … 只会定义一个带有字面值 N 的单个宏;它不会定义一系列带有不同数字替代 N 的宏。

宏不用于循环、任意递归或嵌套。

英文:

The C standard does not specify any dynamic creation of macros. #define FACTORIAL_N(n) … will only define a single macro with a literal N in its name; it will not define a family of macros with different numerals in place of N.

Macros are not intended for looping or arbitrary recursion or nesting.

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  • 本文由 发表于 2023年4月4日 06:18:44
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