Simple exception handling in C11

try_catch.c

#include <errno.h>
#include <setjmp.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
  const char* msg;
  jmp_buf e;
} Ctx;

/*
 * Ctx ctx;
 * TRY(Ctx *ctx) {
 *   // statement...
 * } else {
 *   // exception-handler...
 * }
 */
#define TRY(ctx) if (!setjmp((ctx)->e))

/*
 * raise(Ctx *ctx, const char *fmt, ...) - throw a formatted string as an
 * exception
 */
void raise(Ctx *ctx, const char *fmt, ...) {
  /* construct formatted string */
  va_list ap;
  va_start(ap, fmt);
  int len = vsnprintf(NULL, 0, fmt, ap);
  if (len < 0) {
    fprintf(stderr, "vsnprintf(NULL, 0, fmt, ...):%s\n", strerror(errno));
    exit(1);
  }
  char *buf = malloc(len + 1);
  if (vsnprintf(buf, len + 1, fmt, ap) < 0) {
    fprintf(stderr, "vsnprintf(buf, len, fmt, ...):%s\n", strerror(errno));
    exit(1);
  }
  /* throw as an exception */
  ctx->msg = buf;
  longjmp(ctx->e, -1);
}

void g(Ctx *ctx, int n) {
  int i = 0;
  for (;;) {
    printf("%d", i);
    if (i == n) {
      raise(ctx, "Exception!:%d", i);
    }
    i++;
  }
}

void f(int n) {
  Ctx ctx;
  TRY(&ctx) {                   /* try */
    g(&ctx, n);
  } else {                      /* catch */
    printf("\nException caught:%s\n", ctx.msg);
    free((void *)ctx.msg);
  }
}

int main(int argc, char **argv) {
  for (int i = 0; i < 10; ++i) {
    f(i);
  }
  return 0;
}

Simple exception handling in C. (C++ or Java like try-catch clause)

• Using setjmp() and longjmp()
• A jmp_buf object is encapsulated in a Ctx struct.
• A caller invoke TRY() to setup the jmp_buf object (call setjmp())
• The pointer to a Ctx object is passed to a callee function which may raise a exception.
• By calling raise(), an exception message is composed into the Ctx object and returned to caller.