c语言执行过程不检查数组下标,c语言为什么不数组下标的有效性检查？

最新推荐文章于 2025-02-27 15:29:39 发布

转载最新推荐文章于 2025-02-27 15:29:39 发布 · 157 阅读

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#c语言执行过程不检查数组下标

这篇博客讨论了C语言中指针和数组使用时子数组检查的复杂性。由于标准不要求进行子数组检查，早期和当前大多数编译器都不进行此类检查，这使得在运行时验证指针指向的有效性变得困难。指针可以应用于任意指针，而不仅仅是数组名，这增加了验证的难度。有效性取决于指针当时的指向以及子数组的索引值。因此，C语言中的子数组检查涉及到比初看起来更多的开销，需要插入额外的指令来检查指针是否指向同一数组，并且需要维护所有数组的位置和大小信息，这在运行时会占用时间和空间。

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C和指针，8.1.2

The last two examples show why subscript checking is a difficult task in C.

The standard does not require that it be done at all; the earliest C compilers didn*t check subscripts, and most current ones still don*t.

The fact that subscripts can be applied to arbitrary pointers, not just array names, makes the job difficult.

The validity of a subscript applied to a pointer variable depends on where it happens to be pointing at the time, as well as the value of the subscript.

Consequently, subscript checking in C involves more overhead than you might first think.

Instructions must be inserted into the program to verify that the result of the subscript refers to an element in the same array as the pointer.

This comparison requires information about the locations and sizes of all arrays in the program, which will take some space.

The information must also be updated as the program runs to reflect automatic and dynamically allocated arrays, which will take some time.