7

当我在 Xcode 中分析我的项目时，我得到了一些奇怪的错误。所有这些代码都是单个方法的一部分，该方法创建可用于制作MKAnnotations. 抱歉，如果这是代码泛滥 - 我已尽力注释掉不相关的部分。除了片段之外，我还包括了整个方法，只是为了某种角度。谢谢！

- (void)addLines {
    /*

    NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];

    // Create region and span variables
    MKCoordinateSpan span;
    MKCoordinateRegion region;

    NSArray* arrayOuter = [defaults objectForKey:@"mapSaveDataKey"];

    NSData* data = [arrayOuter objectAtIndex:[[defaults objectForKey:@"currentMap"] intValue]];

    NSArray* arrayOne = [NSKeyedUnarchiver unarchiveObjectWithData:data];

    if (arrayOne.count == 0)
        [self returns:nil];

    */

    NSArray* overlayLat = [arrayOne objectAtIndex:1];
    double lats[overlayLat.count];

    NSArray* overlayLong = [arrayOne objectAtIndex:2];
    double longs[overlayLong.count];

    NSArray* annotationLat = [arrayOne objectAtIndex:8];
    double annotationLats[annotationLat.count];

    NSArray* annotationLong = [arrayOne objectAtIndex:9];
    double annotationsLongs[annotationLong.count];

    /*

    CLLocationCoordinate2D startLocation = CLLocationCoordinate2DMake([[overlayLat objectAtIndex:0] doubleValue], [[overlayLong objectAtIndex:0] doubleValue]);

    CLLocationCoordinate2D finishLocation = CLLocationCoordinate2DMake([[overlayLat objectAtIndex:[overlayLat count] - 1] doubleValue], [[overlayLong objectAtIndex:[overlayLong count] - 1] doubleValue]);

    NSString* string1 = [[[NSString alloc] initWithFormat:@"Lat: %.3f, Long: %.3f", [[overlayLat objectAtIndex:0] doubleValue], [[overlayLong objectAtIndex:0] doubleValue]] autorelease];

    NSString* string2 = [[[NSString alloc] initWithFormat:@"Lat: %.3f, Long: %.3f", [[overlayLat objectAtIndex:([overlayLat count] - 1)] doubleValue], [[overlayLong objectAtIndex:([overlayLong count] - 1)] doubleValue]] autorelease];

    LocationAnnotation* startAnnotation = [[LocationAnnotation alloc] initWithCoordinate:startLocation title:@"Start" subtitle:string1];

    LocationAnnotation* finishAnnotation = [[LocationAnnotation alloc] initWithCoordinate:finishLocation title:@"Finish" subtitle:string2];

    */

    for (int iii = 0; iii < overlayLat.count; iii++) {
        NSNumber* a = (NSNumber*)[overlayLat objectAtIndex:iii];
        lats[iii] = [a doubleValue];
    }

    for (int iii = 0; iii < overlayLong.count; iii++) {
        NSNumber* a = (NSNumber*)[overlayLong objectAtIndex:iii];
        longs[iii] = [a doubleValue];
    }

    for (int iii = 0; iii < annotationLong.count; iii++) {
        NSNumber* a = (NSNumber*)[annotationLong objectAtIndex:iii];
        annotationsLongs[iii] = [a doubleValue];
    }

    for (int iii = 0; iii < annotationLat.count; iii++) {
        NSNumber* a = (NSNumber*)[annotationLat objectAtIndex:iii];
        annotationLats[iii] = [a doubleValue];
    }

    int sizeLats = 0;

    for (int iii = 0; iii < overlayLat.count; iii++)
        if (lats[iii] != 0)
            sizeLats++;

    CLLocationCoordinate2D coords[sizeLats];

    for (int iii = 0; iii < sizeLats; iii++) {
        if (lats[iii] != 0 && longs[iii] != 0) {
            coords[iii].latitude = lats[iii];
            coords[iii].longitude = longs[iii];
        } else {
            coords[iii].latitude = coords[iii - 1].latitude;
            coords[iii].longitude = coords[iii - 1].longitude;
        }
    }

    /*

    // Give variables value
    span = MKCoordinateSpanMake(.05, .05);       
    region = MKCoordinateRegionMake(coords[0], span);

    MKPolyline* line = [MKPolyline polylineWithCoordinates:coords count:sizeLats];

    [mapView addOverlay:line];

    [mapView addAnnotations:[NSArray arrayWithObjects:startAnnotation, finishAnnotation, nil]];
    [mapView selectAnnotation:startAnnotation animated:YES];

    */

    for (int iii = 0; iii < annotationLong.count; iii++) {
        CLLocationCoordinate2D coord = CLLocationCoordinate2DMake(annotationLats[iii], annotationsLongs[iii]);
        /*

        NSString* subtitle = [[[NSString alloc] initWithFormat:@"Lat: %.3f, Long: %.3f", coord.latitude, coord.longitude] autorelease];
        NSString* title = [[[NSString alloc] initWithFormat:@"Stop %i", (iii + 1)] autorelease];
        LocationAnnotation* a = [[LocationAnnotation alloc] initWithCoordinate:coord title:title subtitle:subtitle];
        CLLocation* c = [[CLLocation alloc] initWithCoordinate:coord altitude:0 horizontalAccuracy:0 verticalAccuracy:0 course:0 speed:0 timestamp:0];
        CLLocation* d = [[CLLocation alloc] initWithCoordinate:CLLocationCoordinate2DMake(finishAnnotation.coordinate.latitude, finishAnnotation.coordinate.longitude) altitude:0 horizontalAccuracy:0 verticalAccuracy:0 course:0 speed:0 timestamp:0];
        if ([c distanceFromLocation:d] > 20)
            [mapView addAnnotation:a];
        [c release];
        [d release];
        [a release];

        */
    }

    /*

    [mapView setRegion:region animated:YES];

    [startAnnotation release];
    [finishAnnotation release];

    */
}

第一的：

int sizeLats = 0;

for(int iii = 0; iii < overlayLat.count; iii++)
    if(lats[iii] != 0) //"The left operand of '!=' is a garbage value"
        sizeLats++;

Xcode 怎么敢指责我这种恶作剧？

第二：

CLLocationCoordinate2D coords[sizeLats]; //"Declared variable-length array (VLA) has zero size"

第三：

for (int iii = 0; iii < sizeLats; iii++) {
    if (lats[iii] != 0 && longs[iii] != 0) { // "The left operand of '!=' is a garbage value"
        coords[iii].latitude = lats[iii];
        coords[iii].longitude = longs[iii];
    } else {
        coords[iii].latitude = coords[iii - 1].latitude; // "Assigned value is garbage or undefined"
        coords[iii].longitude = coords[iii - 1].longitude;
    }
}

第四：

CLLocationCoordinate2D coord = CLLocationCoordinate2DMake(annotationLats[iii], annotationsLongs[iii]); // "Function call argument is an uninitialized value"

除了，我刚刚初始化了那个数组？我知道如果annotationLats并且annotationLongs用零长度初始化它可能会未初始化。

这些警告是否重要？如果我的程序在没有这些警告的情况下按预期运行，我可以安全地忽略它们吗？我只是觉得忽略 Xcode 不是一个好主意——它相当聪明。

4

1 回答 1

6

误解是clang/checker不能保证数组count不会改变，也不能确定程序会像你的数组一样流动。

我真正的问题是这些警告是否至关重要，如果我的程序按预期运行，没有错误，（好吧，没有与这些警告相关的错误：D）我可以安全地忽略它们吗？我只是觉得忽略 Xcode 不是一个好主意。它相当聪明。

就我个人而言，我不会忽视它们，并且会努力将这些问题压低。

您可以稍微更改您的程序以与编译器/检查器期望的程序流程保持一致。完成此操作并删除大部分警告的简单方法是引入一个变量来表示您期望无法更改的内容：

NSArray* overlayLat = [arrayOne objectAtIndex:1];
const NSUInteger overlayLatCount = [overlayLat count];
// now use the variable instead of calling the method where needed:
double lats[overlayLatCount];
...

然后使用这些变量而不是方法。当然，您应该小心确保您创建的变量将始终等于它们所代表的值。

还有一些其他位：检查器并不总是知道类型的语义。例如：您可能认为 NSArray 的计数可以被缓存，但检查器必须对许多类了解很多才能理解这些问题。更重要的是，由于许多其他原因，检查器不能保证程序会按照您的预期运行。假设数组的计数作为优化被缓存；这将导致现实世界程序中出现大量错误。因此，当您有检查器可能不依赖的上下文时，您必须使一些事情更加明显——在某些情况下您必须引入该上下文。

第一组问题，更详细

NSArray * overlayLat = [arrayOne objectAtIndex:1];
const NSUInteger overlayLatCount = [overlayLat count];
double lats[overlayLatCount];

NSArray * overlayLong = [arrayOne objectAtIndex:2];
const NSUInteger overlayLongCount = [overlayLong count];
double longs[overlayLongCount];

NSArray * annotationLat = [arrayOne objectAtIndex:8];
const NSUInteger annotationLatCount = [annotationLat count];
double annotationLats[annotationLatCount];

NSArray * annotationLong = [arrayOne objectAtIndex:9];
const NSUInteger annotationLongCount = [annotationLong count];
double annotationsLongs[annotationLongCount];

for (int iii = 0; iii < overlayLatCount; iii++) {
    NSNumber * a = (NSNumber*)[overlayLat objectAtIndex:iii];
    lats[iii] = [a doubleValue];
}

for (int iii = 0; iii < overlayLongCount; iii++) {
    NSNumber * a = (NSNumber*)[overlayLong objectAtIndex:iii];
    longs[iii] = [a doubleValue];
}

for (int iii = 0; iii < annotationLongCount; iii++) {
    NSNumber * a = (NSNumber*)[annotationLong objectAtIndex:iii];
    annotationsLongs[iii] = [a doubleValue];
}

for (int iii = 0; iii < annotationLatCount; iii++) {
    NSNumber * a = (NSNumber*)[annotationLat objectAtIndex:iii];
    annotationLats[iii] = [a doubleValue];
}

其余问题的详细信息

1) 声明的 VLA 大小为零：

含义：检查器看到它sizeLats被初始化为零，并且仅有条件地递增。它警告您数组长度可能为零。

解决方案：在继续之前测试为零：

if (0 == sizeLats) return;

CLLocationCoordinate2D coords[sizeLats];

这是向编译器保证您不会创建或使用零长度 VLA 的一种方法。

2) != 的左操作数是垃圾值：

if ((lats[iii] != 0) && (longs[iii] != 0)) {

含义：检查器不能保证数组已经完全初始化并且sizeLats小于[overlayLat count]和[overlayLong count]。更重要的是，它应该警告超出范围访问的可能性。这个消息不是很清楚。

解决方案：程序中实际上有一些未经检查的界限和假设（并且可能删除了一些错误检查）。这应该让检查器和编译器更清楚。您应该使编译器更清楚这一点，并添加一些错误检测以防万一（将提供更完整的示例）。

附加说明 - 浮点比较不是很安全 - 你不应该期望 C 数组被初始化

3) 函数调用参数是一个未初始化的值。

含义：这个问题的根源与＃2“！=的左操作数是垃圾值”相同。指定索引处的数组可能尚未初始化。更糟糕的问题是不能保证数组索引会在范围内。它没有被标记的事实让我想知道检查器是否由于误报太多而禁用了这个警告。

分辨率：同#2

因此，具有广泛错误检查的更彻底的示例可能会像以下程序一样流动。该程序并不漂亮，可以使用一些清理/重构，但是所有的错误检查都存在，它没有检查器问题就通过了，并且使有问题的代码无法访问并检测到大量错误。我仍然不认为浮点比较或 VLA 很好，但这应该足以解决您的问题。

/**
  @brief fills a double buffer with values from an NSArray
  @param destinationBuffer the buffer to fill
  @param countOfDestinationBuffer the number of elements in @a destinationBuffer
  @param the source values. an NSArray filled with NSNumber objects. @a countOfDestinationBuffer must be equal to @a [source count]
  @return false if an error occurred, else true
*/
static bool FillDoubleArrayFromNSArray(double* const destinationBuffer, const NSUInteger countOfDestinationBuffer, NSArray* source) {
    const NSUInteger sourceCount = [source count];
    if ((0 == destinationBuffer) || (0 == countOfDestinationBuffer) || (0 == [source count])) {
        assert(0 && "invalid argument");
        return false;
    }
    else if (sourceCount != countOfDestinationBuffer) {
        assert(0 && "buffer size mismatch");
        return false;
    }

    for (NSUInteger idx = 0; idx < sourceCount; ++idx) {
        NSNumber* a = (NSNumber*)[source objectAtIndex:idx];
        destinationBuffer[idx] = [a doubleValue];
    }

    return true;
}

- (void)addLines {
    NSArray* arrayOne = [NSArray array];

    NSArray* overlayLatArray = [arrayOne objectAtIndex:1];
    const NSUInteger overlayLatCount = [overlayLatArray count];
    if (0 == overlayLatCount) {
        assert(0 && "empty array or invalid object. bailing.");
        return;
    }

    double lats[overlayLatCount];
    if (!FillDoubleArrayFromNSArray(lats, overlayLatCount, overlayLatArray)) {
    /* do something */
        return;
    }

    NSArray* overlayLongArray = [arrayOne objectAtIndex:2];
    const NSUInteger overlayLongCount = [overlayLongArray count];
    if (0 == overlayLongCount) {
        assert(0 && "empty array or invalid object. bailing.");
        return;
    }

    double longs[overlayLongCount];
    if (!FillDoubleArrayFromNSArray(longs, overlayLongCount, overlayLongArray)) {
    /* do something */
        return;
    }

    NSUInteger sizeLat = 0;
    for (NSUInteger idx = 0; idx < overlayLatCount; ++idx) {
        if (lats[idx] != 0) {
            ++sizeLat;
        }
    }

    if (0 == sizeLat) {
        assert(0 && "what to do when no lines can be drawn?");
        return;
    }

    if ((overlayLatCount < sizeLat) || (overlayLongCount < sizeLat)) {
        assert(0 && "input range error (overlayLongCount is really what we are testing here)");
        return;
    }

    CLLocationCoordinate2D coords[sizeLat];
    for (NSUInteger idx = 0; idx < sizeLat; ++idx) {
        if ((lats[idx] != 0) && (longs[idx] != 0)) {
            coords[idx] = CLLocationCoordinate2DMake(lats[idx], longs[idx]);
        }
        else if (0 == idx) {
            assert(0 && "range error. access of invalid index would have occurred");
            return;
        }
        else {
            coords[idx] = coords[idx - 1];
        }
    }

    NSArray* annotationLatArray = [arrayOne objectAtIndex:8];
    const NSUInteger annotationLatCount = [annotationLatArray count];
    if (0 == annotationLatCount) {
        assert(0 && "empty array or invalid object. bailing.");
        return;
    }

    double annotationLat[annotationLatCount];
    if (!FillDoubleArrayFromNSArray(annotationLat, annotationLatCount, annotationLatArray)) {
    /* do something */
        return;
    }

    NSArray* annotationLongArray = [arrayOne objectAtIndex:9];
    const NSUInteger annotationLongCount = [annotationLongArray count];
    if (0 == annotationLongCount) {
        assert(0 && "empty array or invalid object. bailing.");
        return;
    }

    double annotationLong[annotationLongCount];
    if (!FillDoubleArrayFromNSArray(annotationLong, annotationLongCount, annotationLongArray)) {
    /* do something */
        return;
    }

    if (annotationLatCount < annotationLongCount) {
        assert(0 && "input range error in next loop. bailing");
        return;
    }

    for (NSUInteger idx = 0; idx < annotationLongCount; ++idx) {
        CLLocationCoordinate2D coord = CLLocationCoordinate2DMake(annotationLat[idx], annotationLong[idx]);
/* ... */
    }
}
于 2011-11-03T01:52:21.523 回答