objective-c - 在 Objective-C 中除以零

Question

为什么下面的代码在运行时不会抛出算术错误 -> 1/0;

printf("in start\n");
int i=1/0;
//int o=i;
NSString* myString = [@(i) stringValue];
printf("%s", [myString UTF8String]);
printf("\nafter start\n");

控制台:

in start
-1074745488
after start

Answer 1

它不会抛出错误，因为它是纯 C — 而 C 不知道如何抛出错误。

---

如果你像这样进入Objective-C的客观世界

NSDecimalNumber *i = [NSDecimalNumber decimalNumberWithDecimal:[@(1) decimalValue]];
NSDecimalNumber *o = [NSDecimalNumber decimalNumberWithDecimal:[@(0) decimalValue]];

NSDecimalNumber *x = [i decimalNumberByDividingBy:o];

你会看到

*** Terminating app due to uncaught exception 'NSDecimalNumberDivideByZeroException', reason: 'NSDecimalNumber divide by zero exception'
*** First throw call stack:
(
    0   CoreFoundation                      0x00007fff870cf50c __exceptionPreprocess + 172
    1   libobjc.A.dylib                     0x00007fff8abd076e objc_exception_throw + 43
    2   CoreFoundation                      0x00007fff870cf3bd +[NSException raise:format:] + 205
    3   Foundation                          0x00007fff8a476ec5 -[NSDecimalNumberHandler exceptionDuringOperation:error:leftOperand:rightOperand:] + 242
    4   Foundation                          0x00007fff8a475cab _checkErrorAndRound + 57
    5   Foundation                          0x00007fff8a47606c -[NSDecimalNumber decimalNumberByDividingBy:withBehavior:] + 159
    6   devisonByZero                       0x0000000100000e54 main + 484
    7   libdyld.dylib                       0x00007fff8aaa45c9 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

---

但是您实际上可以决定，会发生什么:

NSDecimalNumberHandler *h = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundPlain
                                                                                   scale:1
                                                                        raiseOnExactness:NO
                                                                         raiseOnOverflow:NO
                                                                        raiseOnUnderflow:NO
                                                                     raiseOnDivideByZero:NO];

NSDecimalNumber *x = [i decimalNumberByDividingBy:o withBehavior:h];

x 现在将是 NaN。

---

但 apple 还提供了可识别计算错误的 C 类型:NSDecimal

NSDecimal one = [@1 decimalValue];
NSDecimal zero = [@0 decimalValue];
NSDecimal result;
NSCalculationError error = NSDecimalDivide(&result, &one, &zero, NSRoundPlain);
switch (error) {
    case NSCalculationNoError:
        NSLog(@"result: %@", [NSDecimalNumber decimalNumberWithDecimal:result]);
        break;
    case NSCalculationDivideByZero:
        NSLog(@"division by 0");
        break;
    default:
        NSLog(@"some calculation error");
        break;
}