Basic implementation of exceptions and scope guards in C using POSIX setjmp/longjmp

jumptest.c

#include <setjmp.h>
#include <stdio.h>
#include <jumptests.h>

static jmp_buf *last_buf  = NULL;
static jmp_buf *scope_buf = NULL;

void second() {
    printf("--> enter second\n");
    throw(1);
    printf("--> exit second\n");
}

void first() {
    printf("--> enter first\n");


    second();
    printf("--> exit first\n");
}

void prima() {

    printf("--> enter prima\n");
    on_exit({
        printf("--> exit prima, first on_exit()\n");
    })
    on_exit({
        printf("--> exit prima, second on_exit()\n");
    })

    try({
        printf("--> from prima, calling second\n");
        second();
    }, {
        printf("--> prima 'catch' block\n");
    })

    second();
    printf("--> exit prima\n");

    frame_end();
}

int main() {

    printf("--> enter main\n");

    try({
        first();
    }, {
        printf("--> main 'catch' block\n");
    })

    prima();
    printf("--> exit main\n");

    frame_end();
    return 0;
}

jumptests.h

#define MERGE_(a,b)  a##b

#define frame_end() \
    if(scope_buf) longjmp(*scope_buf, 1);

#define try_impl(try_block, catch_block, unique) \
    jmp_buf    *MERGE_(_tmp_try_buf_, unique) = last_buf;   \
    jmp_buf     MERGE_(_try_buf_, unique);                  \
    last_buf = &MERGE_(_try_buf_, unique);                  \
    do {                                                    \
        if(setjmp(*last_buf) == 0) {                        \
            try_block;                                      \
        } else {                                            \
            catch_block;                                    \
        }                                                   \
    } while(0);                                             \
    last_buf = MERGE_(_tmp_try_buf_, unique);

#define try(try_block, catch_block) \
    try_impl(try_block, catch_block, __LINE__)

#define throw(val) longjmp(*last_buf, val)

#define on_exit_impl(exit_block, unique)                        \
    jmp_buf MERGE_(_scope_buf_, unique);                        \
    jmp_buf *MERGE_(_tmp_scope_last_buf_, unique) = last_buf;   \
    jmp_buf *MERGE_(_tmp_scope_scope_buf_, unique) = scope_buf; \
    last_buf  = &MERGE_(_scope_buf_, unique);                   \
    scope_buf = &MERGE_(_scope_buf_, unique);                   \
    do {                                                        \
        if(setjmp(*scope_buf) != 0) {                           \
            exit_block;                                         \
            last_buf  = MERGE_(_tmp_scope_last_buf_, unique);   \
            scope_buf = MERGE_(_tmp_scope_scope_buf_, unique);  \
            if(scope_buf) { longjmp(*scope_buf, 1); }           \
            else { return; }                                    \
        }                                                       \
    } while(0);

#define on_exit(exit_block) \
    on_exit_impl(exit_block, __LINE__)

stdout

--> enter main
--> enter first
--> enter second
--> main 'catch' block
--> enter prima
--> from prima, calling second
--> enter second
--> prima 'catch' block
--> enter second
--> exit prima, second on_exit()
--> exit prima, first on_exit()
--> exit main