June 19th Friday (六月　十九日　木曜日)

There is try/except implemented in C program languages. It can be used in sources in C language.
From it, we can learn how to use macro in C and the principle of try/except.

//except.h
#ifndef EXCEPT_INCLUDED
#define EXCEPT_INCLUDED
#include <setjmp.h>
#define T Except_T
typedef struct T {
char *reason;
} T;
typedef struct Except_Frame Except_Frame;
struct Except_Frame {
Except_Frame *prev;
jmp_buf env;
const char *file;
int line;
const T *exception;
};
enum { Except_entered=0, Except_raised,
Except_handled, Except_finalized };
#ifdef WIN32
__declspec(thread)
#endif
extern Except_Frame *Except_stack;
extern const Except_T Assert_Failed;
void Except_raise(const T *e, const char *file,int line);
#define RAISE(e) Except_raise(&(e), __FILE__, __LINE__)
#define RERAISE Except_raise(Except_frame.exception, /
Except_frame.file, Except_frame.line)
#define RETURN switch (Except_stack = Except_stack->prev,0) default: return
#define TRY do { /
volatile int Except_flag; /
Except_Frame Except_frame; /
Except_frame.prev = Except_stack; /
Except_stack = &Except_frame; /
Except_flag = setjmp(Except_frame.env); /
if (Except_flag == Except_entered) {
#define EXCEPT(e) /
if (Except_flag == Except_entered) Except_stack = Except_stack->prev; /
} else if (Except_frame.exception == &(e)) { /
Except_flag = Except_handled;
#define ELSE /
if (Except_flag == Except_entered) Except_stack = Except_stack->prev; /
} else { /
Except_flag = Except_handled;
#define FINALLY /
if (Except_flag == Except_entered) Except_stack = Except_stack->prev; /
} { /
if (Except_flag == Except_entered) /
Except_flag = Except_finalized;
#define END_TRY /
if (Except_flag == Except_entered) Except_stack = Except_stack->prev; /
} if (Except_flag == Except_raised) RERAISE; /
} while (0)
#undef T
#endif

//except.cpp
static char rcsid[] = "$Id: H:/drh/idioms/book/RCS/except.doc,v 1.10 1997/02/21 19:43:55 drh Exp $";
#include <stdlib.h>
#include <stdio.h>
#include "assert.h"
#include "except.h"
#define T Except_T
#ifdef WIN32
__declspec(thread)
#endif
Except_Frame *Except_stack = NULL;
void Except_raise(const T *e, const char *file,
int line) {
Except_Frame *p = Except_stack;
assert(e);
if (p == NULL) {
fprintf(stderr, "Uncaught exception");
if (e->reason)
fprintf(stderr, " %s", e->reason);
else
fprintf(stderr, " at 0x%p", e);
if (file && line > 0)
fprintf(stderr, " raised at %s:%d/n", file, line);
fprintf(stderr, "aborting.../n");
fflush(stderr);
abort();
}
p->exception = e;
p->file = file;
p->line = line;
Except_stack = Except_stack->prev;
longjmp(p->env, Except_raised);
}