TAILIEUCHUNG - Lập trình Wrox Professional Xcode 3 cho Mac OS part 63

Kiểm tra dữ liệu Bây giờ bạn đã học được tất cả về việc kiểm soát dòng chảy của các ứng dụng của bạn trong khi gỡ lỗi, chúng ta hãy quay lại kiểm tra các nội dung của các biến. "Những biến Cửa sổ" phần giới thiệu tóm tắt cửa sổ biến của các cửa sổ gỡ rối. | 480 CHAPTER 18 DEBUGGING EXAMINING DATA Now that you ve learned all about controlling the flow of your application while debugging let s return to examining the content of variables. The Variables Pane section briefly introduced the variables pane of the debugging window. Now look at that pane in a little more detail and look at other ways of examining the contents of memory. To recap the variables pane previously shown in Figure 18-4 displays the known variables within the scope of the selected stack frame. Variables are grouped by type. Structures and objects appear as groups forming a hierarchy of containers and values. These are described by the debug symbol information attached to your program. As you step through your program the debugger compares the values that were displayed when your program was last started against the values that appear when the debugger stopped it again. Any values that are different are highlighted in red as shown in Figure 18-26 it may be difficult to see in this black-and-white illustration but the value of variable j is red. The code was stopped at line 57 where the value of j was undefined. The Step Over command was issued. The debugger allowed one statement the for statement to be executed and stopped the program again. The value of j is now 4 and Xcode highlights the change in the display. Using the Step Over command again returns the value to black again because that statement did not alter its value. It doesn t matter how much the program executes between stops. As long as the variables pane is showing the same set of variables at the next stop Xcode highlights whatever values are now different. Scalar Formats The Value column displays the primitive value of each variable. For scalar values this is a numeric value. For structures and pointers to structures it is the address of the structure or the value of the pointer. The default display format for scalar values is Natural. For signed integers and floatingpoint numbers the .

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• xcode
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