objective-c - EXC_BAD_ACCESS 中的code=1 和code=2 有什么区别？

Question

我收到 code=1 或 code=2 的 EXC_BAD_ACCESS 错误。我想知道 code=1 和 code=2 之间有什么区别？

Answer 1

代码 = 1 是 KERN_INVALID_ADDRESS，代码 = 2 是 KERN_PROTECTION_FAILURE。两者都是在 "Technical Note TN2123 CrashReporter" 中解释:

The most common forms of exception are:

• EXC_BAD_ACCESS/KERN_INVALID_ADDRESS — This is caused by the thread accessing unmapped memory. It may be triggered by either a data access or an instruction fetch; the Thread State section describes how to tell the difference.
• EXC_BAD_ACCESS/KERN_PROTECTION_FAILURE — This is caused by the thread trying to write to read-only memory. This is always caused by a data access.

代码在 <mach/kern_return.h> 中定义:

#define KERN_INVALID_ADDRESS            1
                /* Specified address is not currently valid.
                 */

#define KERN_PROTECTION_FAILURE         2
                /* Specified memory is valid, but does not permit the
                 * required forms of access.
                 */

在 <mach/exception_types.h> 中据记载，代码对于 EXC_BAD_ACCESS 是 kern_return_t :

#define EXC_BAD_ACCESS          1       /* Could not access memory */
                /* Code contains kern_return_t describing error. */
                /* Subcode contains bad memory address. */