/* * File: exception.c * Last modified on Sun Jul 24 10:28:11 1994 by eroberts * ----------------------------------------------------- * This file implements the C exception handler.  Much of the * real work is done in the exception.h header file. */#include <stdio.h>#include <stdarg.h>#include "genlib.h"#include "gcalloc.h"#include "exception.h"/* * Constant: MaxUnhandledMessage * ----------------------------- * This constant should be large enough to accommodate the * unhandled exception message, including the exception name. */#define MaxUnhandledMessage 100/* Publically accessible exceptions */exception ANY = { "ANY" };exception ErrorException = { "ErrorException" };/* * Global variable: exceptionStack * ------------------------------- * This variable is the head pointer to a linked list of * context blocks that act as the exception stack.  The chain * pointer is referenced by the macros in exception.h and must * therefore be exported, but clients should not reference it * directly. */context_block *exceptionStack = NULL;/* Private function prototypes */static context_block *FindHandler(exception *e);/* Public entries *//* * Function: RaiseException * ------------------------ * This function operates by finding an appropriate handler * and then using longjmp to return to the context stored * there after resetting the exception stack.  If no handler * exists, the function notes an unhandled exception.  Much * of the complexity comes from the fact that allocation * within the exception handler may fail. */void RaiseException(exception *e, string name, void *value){    context_block *cb;    char errbuf[MaxUnhandledMessage + 1];    string errmsg;    int errlen;    cb = FindHandler(e);    if (cb == NULL) {        sprintf(errbuf, "Unhandled exception (%.30s)", name);        errlen = strlen(errbuf);        if (_acb == NULL) {            errmsg = malloc(errlen + 1);        } else {            errmsg = _acb->allocMethod(errlen + 1);        }        if (errmsg == NULL) {            errmsg = "Unhandled exception: unknown";        } else {            strcpy(errmsg, errbuf);        }        Error(errmsg);    }    exceptionStack = cb;    cb->id = e;    cb->value = value;    cb->name = name;    longjmp(cb->jmp, ES_Exception);}/* * Function: HandlerExists * ----------------------- * This public entry is used primarily by the Error function * to determine if ErrorException has been trapped, although * it is available to other clients as well. */bool HandlerExists(exception *e){    return (FindHandler(e) != NULL);}/* Private functions *//* * Function: FindHandler * --------------------- * This function searches the exception stack to find the * first active handler for the indicated exception.  If a * match is found, the context block pointer is returned. * If not, FindHandler returns NULL. */static context_block *FindHandler(exception *e){    context_block *cb;    exception *t;    int i;    for (cb = exceptionStack; cb != NULL; cb = cb->link) {        for (i = 0; i < cb->nx; i++) {            t = cb->array[i];            if (t == e || t == &ANY) return (cb);        }    }    return (NULL);}