The StringLengthFromMode function calculates the length of a null-terminated string, based on the specified processor mode.
Syntax
SIZE_T StringLengthFromMode(
const CHAR *String,
KPROCESSOR_MODE Mode
);
Parameters
String
[in]指向以 null 结尾的字符串的指针。
Mode
[in]确定内存访问的执行方式的处理器模式。 Mode can be one of the following values.
| Value | Meaning |
|---|---|
| KernelMode | String points to kernel-mode memory. 该函数执行直接字符串长度计算。 有关更多详细信息，请参阅“备注”。 |
| UserMode | String points to user-mode memory. The function raises an exception if String doesn't point to user-mode memory; otherwise it performs a safe string length calculation at the specified address. 有关更多详细信息，请参阅“备注”。 |
Return value
该函数以字符为单位返回字符串的长度，不包括终止 null 字符。
Remarks
此函数提供安全访问，用于计算内存中以 null 结尾的字符串的长度。 行为取决于指定的处理器模式：
- When Mode is UserMode, the function ensures that the string address is a valid user-mode address and performs the operation safely for user-mode memory access.
- When Mode is KernelMode, the function operates directly on kernel-mode addresses.
When the mode is UserMode, the function includes validation to prevent kernel crashes when accessing potentially invalid user-mode pointers. When the mode is KernelMode, it operates on known-safe kernel addresses for optimal performance.
如果作失败，函数将引发结构化异常，例如当字符串地址不可访问或指定模式无效时。
此函数适用于所有版本的 Windows，而不仅仅是最新版本。 You need to consume the latest WDK to get the function declaration from the usermode_accessors.h header. You also need the library (umaccess.lib) from the latest WDK. 但是，生成的驱动程序将在较旧版本的 Windows 上运行。
Requirements
| Requirement | Value |
|---|---|
| 最低支持的客户端 | See Remarks |
| Header | usermode_accessors.h |
| Library | umaccess.lib |
| IRQL | 小于或等于APC_LEVEL |