C macro templace abuse

#include <stdio.h>
#define swap(T,x,y) ({T tmp = (x); (x) = (y); (y) = tmp;})

int main() {
    int x = 2, y = 5;

    swap(int, x, y);
    printf("x = %d, y = %d", x, y); //x = 5, y = 2
    return 0;
}

Is this bad practice?

>>1
Is this bad practice?
Yes. That is not a proper ENTERPRISE implementation.

void.h C11 Enterprise Extensions Version
[code]
/**
 * VOID.H C11 ENTERPRISE EXTENSIONS
 */

#ifndef VOIDEE_H
#define VOIDEE_H

#define swap(x, y) _Generic((x), \
        _Bool*: swap_bool, \
        char*: swap_char, \
        signed char*: swap_schar, \
        short*: swap_short, \
        int*: swap_int, \
        long*: swap_long, \
        long long*: swap_llong, \
        unsigned char*: swap_uchar, \
        unsigned short*: swap_ushort, \
        unsigned int*: swap_uint, \
        unsigned long*: swap_ulong, \
        unsigned long long*: swap_ullong, \
        float*: swap_float, \
        double*: swap_double, \
        long double*: swap_ldouble)(x, y)

inline void swap_bool(_Bool* x, _Bool* y) {
    _Bool t = *x;
    *x = *y;
    *y = t;
}

inline void swap_char(char* x, char* y) {
    char t = *x;
    *x = *y;
    *y = t;
}

inline void swap_schar(signed char* x, signed char* y) {
    signed char t = *x;
    *x = *y;
    *y = t;
}

inline void swap_short(short* x, short* y) {
    short t = *x;
    *x = *y;
    *y = t;
}

inline void swap_int(int* x, int* y) {
    int t = *x;
    *x = *y;
    *y = t;
}

inline void swap_long(long* x, long* y) {
    long t = *x;
    *x = *y;
    *y = t;
}

inline void swap_llong(long long* x, long long* y) {
    long long t = *x;
    *x = *y;
    *y = t;
}

inline void swap_uchar(unsigned char* x, unsigned char* y) {
    unsigned char t = *x;
    *x = *y;
    *y = t;
}

inline void swap_ushort(unsigned short* x, unsigned short* y) {
    unsigned short t = *x;
    *x = *y;
    *y = t;
}

inline void swap_uint(unsigned int* x, unsigned int* y) {
    unsigned int t = *x;
    *x = *y;
    *y = t;
}

inline void swap_ulong(unsigned long* x, unsigned long* y) {
    unsigned long t = *x;
    *x = *y;
    *y = t;
}

inline void swap_ullong(unsigned long long* x, unsigned long long* y) {
    unsigned long long t = *x;
    *x = *y;
    *y = t;
}

inline void swap_float(float* x, float* y) {
    float t = *x;
    *x = *y;
    *y = t;
}

inline void swap_double(double* x, double* y) {
    double t = *x;
    *x = *y;
    *y = t;
}

inline void swap_ldouble(long double* x, long double* y) {
    long double t = *x;
    *x = *y;
    *y = t;
}

#endif

/**
 * VOID.H C11 ENTERPRISE EXTENSIONS EXAMPLE CODE
 */

#include <voidee.h>
#include <stdio.h>

int main() {
    int x = 2, y = 5;
    swap(&x, &y);
    printf("x = %d, y = %d", x, y); //x = 5, y = 2
    return 0;
}>>1
>>1
>>1

>>2
Looks like I found a new way to break Shiichan!

/**
 * VOID.H C11 ENTERPRISE EXTENSIONS
 */

#ifndef VOIDEE_H
#define VOIDEE_H

#define swap(x, y) _Generic((x), \
        _Bool*: swap_bool, \
        char*: swap_char, \
        signed char*: swap_schar, \
        short*: swap_short, \
        int*: swap_int, \
        long*: swap_long, \
        long long*: swap_llong, \
        unsigned char*: swap_uchar, \
        unsigned short*: swap_ushort, \
        unsigned int*: swap_uint, \
        unsigned long*: swap_ulong, \
        unsigned long long*: swap_ullong, \
        float*: swap_float, \
        double*: swap_double, \
        long double*: swap_ldouble)(x, y)

inline void swap_bool(_Bool* x, _Bool* y) {
    _Bool t = *x;
    *x = *y;
    *y = t;
}

inline void swap_char(char* x, char* y) {
    char t = *x;
    *x = *y;
    *y = t;
}

inline void swap_schar(signed char* x, signed char* y) {
    signed char t = *x;
    *x = *y;
    *y = t;
}

inline void swap_short(short* x, short* y) {
    short t = *x;
    *x = *y;
    *y = t;
}

inline void swap_int(int* x, int* y) {
    int t = *x;
    *x = *y;
    *y = t;
}

inline void swap_long(long* x, long* y) {
    long t = *x;
    *x = *y;
    *y = t;
}

inline void swap_llong(long long* x, long long* y) {
    long long t = *x;
    *x = *y;
    *y = t;
}

inline void swap_uchar(unsigned char* x, unsigned char* y) {
    unsigned char t = *x;
    *x = *y;
    *y = t;
}

inline void swap_ushort(unsigned short* x, unsigned short* y) {
    unsigned short t = *x;
    *x = *y;
    *y = t;
}

inline void swap_uint(unsigned int* x, unsigned int* y) {
    unsigned int t = *x;
    *x = *y;
    *y = t;
}

inline void swap_ulong(unsigned long* x, unsigned long* y) {
    unsigned long t = *x;
    *x = *y;
    *y = t;
}

inline void swap_ullong(unsigned long long* x, unsigned long long* y) {
    unsigned long long t = *x;
    *x = *y;
    *y = t;
}

inline void swap_float(float* x, float* y) {
    float t = *x;
    *x = *y;
    *y = t;
}

inline void swap_double(double* x, double* y) {
    double t = *x;
    *x = *y;
    *y = t;
}

inline void swap_ldouble(long double* x, long double* y) {
    long double t = *x;
    *x = *y;
    *y = t;
}

#endif

/**
 * VOID.H C11 ENTERPRISE EXTENSIONS EXAMPLE CODE
 */

#include <voidee.h>
#include <stdio.h>

int main() {
    int x = 2, y = 5;
    swap(&x, &y);
    printf("x = %d, y = %d", x, y); //x = 5, y = 2
    return 0;
}

>>2
lol

>>1
Personally, I'd just write a generic function, since it will work with arrays and structs as well (and I guess I just prefer using functions over macros). Aside from that, I don't think there's anything largely wrong with what you're doing.

#include <stdio.h>

static void *swap(void *v1, void *v2, size_t size)
{
    char *a = v1;
    char *b = v2;

    while (size--) {
        char tmp = *a;

        *a++ = *b;
        *b++ = tmp;
    }
    return v1;
}

int main(void)
{
    int x = 2;
    int y = 5;

    swap(&x, &y, sizeof x);
    printf("x = %d, y = %d\n", x, y);
    return 0;
}

>>5
Rename your function swapmem, and you have a winner.

>>6
Or memswap, I mean.

>>7
'mem' followed by a lower case letter is a reserved name in GNU libc.

http://www.gnu.org/software/libc/manual/html_node/Reserved-Names.html

>>7
or maybe even swapsperm

>>5
just add a little #define SWAP(x, y) swap(&(x), &(y), sizeof(x))
and you're good to go.

>>9
swaps perm? this has nothing to do with permissions

>>5
This breaks under certain conditions.

Yes, OP, it is bad practice.


    int x = 2, y = 5;
    swap(int, x++, y++); // OH SHI~

Here's how a popular C library implements it.


void generic_swap(void * a, void * b, size_t n)
{
  int counter = 0;

  for(counter = 0; counter < n; ++counter)
  {
    *( ((BYTE *) a) + counter) ^= *( ((BYTE *) b) + counter);
    *( ((BYTE *) b) + counter) ^= *( ((BYTE *) a) + counter);
    *( ((BYTE *) a) + counter) ^= *( ((BYTE *) b) + counter);
  }
}

template<class T> void swap(T& a, T& b) {
    T tmp = a;
    a = b;
    b = tmp;
}

test

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