how can I avoid the use of #if in a polymorphic print macro
Let\'s try to run the following code:
#include
#define MY_MACRO1(isArray,y) do { \\
if(isArray) \\
-
Is there anyway to call a #if statement inside a macro?
Not possible.
if not, how can I do such a thing?
You could use C11 _Generic:
#include <stdio.h> void int_func (int obj) { printf("%d\n", obj); } void int_arr_func (const int* obj) { printf("%d\n", obj[0]); } void float_func (float obj) { printf("%f\n", obj); } #define MY_MACRO2(y) _Generic((y), \ int: int_func, \ int*: int_arr_func, \ float: float_func ) (y) int main (void) { int a = 38; int b[]={42}; float pi = 3.14f; MY_MACRO2(a); MY_MACRO2(b); MY_MACRO2(pi); return 0; }讨论(0) -
You can use BOOST_PP_IF:
#include <boost/preprocessor/if.hpp> #define MY_MACRO1(isArray,y) printf("%d", BOOST_PP_IF(isArray, (y)[0], (y)))See it live on Coliru
讨论(0) -
Let me first say that I don't think you should use macro for this. You should have 2 separate functions instead, with possibly additional
_Genericexpression as shown in Lundins answer.However, it is possible to do with multiple macro defines:
#define MY_MACRO(isArray,y) MY_MACRO_ ## isArray (y) #define MY_MACRO_0(y) printf("%d", y) #define MY_MACRO_1(y) printf("%d", y[0])讨论(0) -
Sum up and another works around using VLA & macros.
Using _Generic
#include <assert.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <stdint.h> static inline void printNonArray_u32 (uint32_t obj) { printf("interger >> uint32_t : %u\n",obj); } static inline void printNonArray_u16 (uint16_t obj) { printf("interger >> uint16_t : %u\n",obj); } static inline void printNonArray_u8 (uint8_t obj) { printf("interger >> uint8_t : %d\n",obj); } static inline void printArray_u32 (const uint32_t* obj) { printf("array >> uint32_t : "); for(uint32_t i = 0 ; i<sizeof(obj)/sizeof(uint32_t) ; i++ ) printf("%d - ",(uint32_t)obj[i]); printf("\n"); } static inline void printArray_u16 (const uint16_t* obj) { printf("array >> uint16_t : "); for(uint32_t i = 0 ; i<sizeof(obj)/sizeof(uint16_t) ; i++ ) printf("%d - ",(uint16_t)obj[i]); printf("\n"); } static inline void printArray_u8(const uint8_t* obj) { printf("array >> uint8_t : "); for(uint32_t i = 0 ; i<sizeof(obj)/sizeof(uint8_t) ; i++ ) printf("%d - ",(uint8_t)obj[i]); printf("\n"); } #define MY_POLYMORPHIC_PRINT2(y) _Generic((y), \ uint32_t: printNonArray_u32, \ uint32_t*: printArray_u32, \ uint16_t: printNonArray_u16, \ uint16_t*: printArray_u16, \ uint8_t: printNonArray_u8, \ uint8_t*: printArray_u8 ) (y) int main() { uint32_t i1 = 257; uint16_t i2 = 257; uint8_t i3 = 25; uint32_t a1[]={42,43,44,257}; uint16_t a2[]={22,23,24,257}; uint8_t a3[]={12,13,14,25}; printf("MY_POLYMORPHIC_PRINT2 - _Generic\n"); MY_POLYMORPHIC_PRINT2(i1); //interger >> uint32_t : 257 >> OK MY_POLYMORPHIC_PRINT2(i2); //interger >> uint16_t : 257 >> OK MY_POLYMORPHIC_PRINT2(i3); //interger >> uint8_t : 25 >> OK MY_POLYMORPHIC_PRINT2(a1); //array >> uint32_t : 42 - 43 - >> FAILS MY_POLYMORPHIC_PRINT2(a2); //array >> uint16_t : 22 - 23 - 24 - 257 - >> OK MY_POLYMORPHIC_PRINT2(a3); //array >> uint8_t : 12 - 13 - 14 - 25 - 253 - 127 - 0 - 0 - >> FAILS return 0; }pros:
- simple macro + simple functions
- you don't need C++ library
- you don't need "isArray" anymore
- you don't need #if
- type-safe
cons:
- how to get the array size? --> gives some bad results without
- limited to C11
Using VLA (no ##)
#include <assert.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <stdint.h> #define MY_POLYMORPHIC_PRINT1(y, type) do { \ if((sizeof(y)/sizeof(type) != 1) && (sizeof(y)/sizeof(type) != sizeof(y))) \ { \ type arrayBuffer[sizeof(y)/sizeof(type)]; \ memcpy(&arrayBuffer,&y,sizeof(y)); \ printf("array >> "#type" : "); \ for(uint32_t i = 0 ; i<sizeof(y)/sizeof(type) ; i++ ) \ printf("%d - ",arrayBuffer[i]); \ printf("\n"); \ } \ else \ { \ type intBuffer = (type)*((type*)(&y)); \ printf("integer >> "#type" : %d\n",intBuffer); \ } \ }while(0) int main() { uint32_t i1 = 257; uint16_t i2 = 257; uint8_t i3 = 25; uint32_t a1[]={42,43,44,257}; uint16_t a2[]={22,23,24,257}; uint8_t a3[]={12,13,14,25}; printf("MY_POLYMORPHIC_PRINT1 - VLA\n"); MY_POLYMORPHIC_PRINT1(i1,uint32_t);// integer >> uint32_t : 257 >> OK MY_POLYMORPHIC_PRINT1(i2,uint16_t);// integer >> uint16_t : 257 >> OK MY_POLYMORPHIC_PRINT1(i3,uint8_t); // integer >> uint8_t : 25 >> OK MY_POLYMORPHIC_PRINT1(i1,uint8_t); // integer >> uint8_t : 1 >> POK wrong type, casting is working MY_POLYMORPHIC_PRINT1(a1,uint32_t);// array >> uint32_t : 42 - 43 - 44 - 257 - >> OK MY_POLYMORPHIC_PRINT1(a2,uint16_t);// array >> uint16_t : 22 - 23 - 24 - 257 - >> OK MY_POLYMORPHIC_PRINT1(a3,uint8_t); // integer >> uint8_t : 12 >> FAILS MY_POLYMORPHIC_PRINT1(a1,uint16_t); // integer >> uint16_t : 42 - 0 - 43 - 0 - 44 - 0 - 257 - 0 - >> POK wrong type, casting is somewhat working return 0; }pros:
- flexible
- compatibility : C99, C11 (VLA option), ...
- just one (ugly) macro
- you don't need C++ library
- you don't need "isArray" anymore
- you don't need array size as an argument
- you don't need #if
cons:
- not type-safe --> gives some bad results
- not compatible before C99
- need type info
Using VLA + ## (string concatenation macro)
#include <assert.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <stdint.h> #define MY_VLA_PRINT_ARRAY(y, type) do{\ type arrayBuffer[sizeof(y)/sizeof(type)]; \ memcpy(&arrayBuffer,&y,sizeof(y)); \ printf("array >> "#type" : "); \ for(uint32_t i = 0 ; i<sizeof(y)/sizeof(type) ; i++ ) \ printf("%d - ",arrayBuffer[i]); \ printf("\n"); \ }while(0) #define MY_VLA_PRINT_NOT_ARRAY(y, type) do{\ type intBuffer = (type)*((type*)(&y)); \ printf("integer >> "#type" : %d\n",intBuffer); \ }while(0) #define MY_POLYMORPHIC_PRINT3( y, isArray, type) do { \ MY_VLA_PRINT_ ## isArray (y, type); \ }while(0) int main() { uint32_t i1 = 257; uint16_t i2 = 257; uint8_t i3 = 25; uint32_t a1[]={42,43,44,257}; uint16_t a2[]={22,23,24,257}; uint8_t a3[]={12,13,14,25}; printf("MY_POLYMORPHIC_PRINT3 - ## + VLA\n"); MY_POLYMORPHIC_PRINT3(i1,NOT_ARRAY,uint32_t); // integer >> uint32_t : 257 >> OK MY_POLYMORPHIC_PRINT3(i2,NOT_ARRAY,uint16_t); // integer >> uint16_t : 257 >> OK MY_POLYMORPHIC_PRINT3(i3,NOT_ARRAY,uint8_t); // integer >> uint8_t : 25 >> OK MY_POLYMORPHIC_PRINT3(i1,NOT_ARRAY,uint8_t); // integer >> uint8_t : 1 >> POK wrong type, casting is working MY_POLYMORPHIC_PRINT3(i1,ARRAY,uint8_t); // array >> uint8_t : 1 - 1 - 0 - 0 - >> POK (does not crash) MY_POLYMORPHIC_PRINT3(a1,ARRAY,uint32_t); // array >> uint32_t : 42 - 43 - 44 - 257 - >> OK MY_POLYMORPHIC_PRINT3(a2,ARRAY,uint16_t); // array >> uint16_t : 22 - 23 - 24 - 257 - >> OK MY_POLYMORPHIC_PRINT3(a3,ARRAY,uint8_t); // array >> uint8_t : 12 - 13 - 14 - 25 - >> OK MY_POLYMORPHIC_PRINT3(a1,ARRAY,uint16_t); // array >> uint16_t : 42 - 0 - 43 - 0 - 44 - 0 - 257 - 0 - >> POK wrong type, casting is somewhat working MY_POLYMORPHIC_PRINT3(a1,NOT_ARRAY,uint16_t); // integer >> uint16_t : 42 >> POK (does not crash) return 0; }pros:
- only solution that works for all test cases
- quite simple macros
- you don't need C++ library
- you don't need #if
cons:
- not compatible before C99
- need isArray
- need type info
- is not type-safe --> but did not give some too bad results
macro ## without VLA:
#include <assert.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <stdint.h> #define MY_NON_VLA_PRINT_ARRAY_U32(y) do{\ printf("array >> uint32_t : "); \ for(uint32_t i = 0 ; i< sizeof(y) / sizeof(uint32_t) ; i++ ) \ printf("%d - ",(uint32_t)*((uint32_t*)&y+(uint32_t*)i)); \ printf("\n"); \ }while(0) #define MY_NON_VLA_PRINT_ARRAY_U16(y) do{\ printf("array >> uint16_t : "); \ for(uint32_t i = 0 ; i< sizeof(y) / sizeof(uint16_t) ; i++ ) \ printf("%d - ",(uint16_t)*((uint16_t*)&y+(uint16_t*)i)); \ printf("\n"); \ }while(0) #define MY_NON_VLA_PRINT_ARRAY_U8(y) do{\ printf("array >> uint8_t : "); \ for(uint32_t i = 0 ; i< sizeof(y) / sizeof(uint8_t) ; i++ ) \ printf("%d - ",(uint8_t)*((uint8_t*)&y+(uint8_t*)i)); \ printf("\n"); \ }while(0) #define MY_NON_VLA_PRINT_NOT_ARRAY_U32(y) do{\ printf("integer >> uint32_t : %d\n",(uint32_t)y); \ }while(0) #define MY_NON_VLA_PRINT_NOT_ARRAY_U16(y) do{\ printf("integer >> uint16_t : %d\n",(uint16_t)y); \ }while(0) #define MY_NON_VLA_PRINT_NOT_ARRAY_U8(y) do{\ printf("integer >> uint8_t : %d\n",(uint8_t)y); \ }while(0) #define MY_POLYMORPHIC_PRINT4( y, isArray, type) do { \ MY_NON_VLA_PRINT_ ## isArray ## _ ## type (y); \ }while(0) int main() { uint32_t i1 = 257; uint16_t i2 = 257; uint8_t i3 = 25; uint32_t a1[]={42,43,44,257}; uint16_t a2[]={22,23,24,257}; uint8_t a3[]={12,13,14,25}; printf("MY_POLYMORPHIC_PRINT4 - ## + no VLA\n"); MY_POLYMORPHIC_PRINT4(i1,NOT_ARRAY,U32); MY_POLYMORPHIC_PRINT4(i2,NOT_ARRAY,U16); MY_POLYMORPHIC_PRINT4(i3,NOT_ARRAY,U8); MY_POLYMORPHIC_PRINT4(i1,NOT_ARRAY,U8); MY_POLYMORPHIC_PRINT4(i1,ARRAY,U8); MY_POLYMORPHIC_PRINT4(a1,ARRAY,U32); MY_POLYMORPHIC_PRINT4(a2,ARRAY,U16); MY_POLYMORPHIC_PRINT4(a3,ARRAY,U8); MY_POLYMORPHIC_PRINT4(a1,ARRAY,U16); MY_POLYMORPHIC_PRINT4(a1,NOT_ARRAY,U16); //does not compile: // error: invalid operands to binary + (have ‘uint32_t * {aka unsigned int *}’ and ‘uint32_t * {aka unsigned int *}’) // printf("%d - ",(uint32_t)*((uint32_t*)&y+(uint32_t*)i)); \ // error: invalid operands to binary + (have ‘uint16_t * {aka short unsigned int *}’ and ‘uint16_t * {aka short unsigned int *}’) // printf("%d - ",(uint16_t)*((uint16_t*)&y+(uint16_t*)i)); \ // error: invalid operands to binary + (have ‘uint8_t * {aka unsigned char *}’ and ‘uint8_t * {aka unsigned char *}’) // printf("%d - ",(uint8_t)*((uint8_t*)&y+(uint8_t*)i)); \ return 0; }pros:
- would be compatible before C99
- you don't need C++ library
- you don't need #if
cons:
- does not compile!
- a lot of macros
- need isArray
- need type info
- is not type-safe
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