如何修复ArrayList兼容UNICODE_STRING时的结构体比较语法错误？

Hey there! Let's get that C2088 error sorted out. The problem is pretty straightforward once you break down why it's happening.

Why You're Getting the Error #

In C, you can't use the == operator directly on structs like UNICODE_STRING—the compiler doesn't know how to automatically compare all the members of a composite type. Your original code worked with an int because that's a primitive value, but UNICODE_STRING has multiple fields (Length, MaximumLength, Buffer), so the direct == check throws that "illegal use of '==' on struct" error.

Solution: Use a Custom Comparison Function #

You need to replace the direct == check with a function that properly compares the two UNICODE_STRING structs. Here are two reliable approaches depending on your environment:

Option 1: Use Windows' Built-in Function (Kernel/User Mode) #

Since you're working with UNICODE_STRING (a Windows-specific type), you can use the RtlEqualUnicodeString function from the Windows API. It safely compares two UNICODE_STRING instances by checking lengths first, then verifying buffer contents.

First, ensure you have the right headers (kernel mode uses ntddk.h; user mode may need winternl.h). Then update your indexOf function:

int indexOf(ArrayList* list, UNICODE_STRING data) {
    for (int index = 0; index < list->size; index++) {
        // Replace == with the built-in comparison function
        if (RtlEqualUnicodeString(&data, &list->elements[index].data, TRUE)) {
            // TRUE = case-insensitive; use FALSE for case-sensitive comparison
            return index;
        }
    }
    return -1;
}

Option 2: Implement Your Own Comparison Function #

If you can't rely on the Windows built-in function, write a custom helper to compare the structs manually:

BOOL AreUnicodeStringsEqual(const UNICODE_STRING* str1, const UNICODE_STRING* str2) {
    // First check if lengths match (bytes, not characters)
    if (str1->Length != str2->Length) {
        return FALSE;
    }
    // Empty strings are equal
    if (str1->Length == 0) {
        return TRUE;
    }
    // Compare the actual buffer content
    return memcmp(str1->Buffer, str2->Buffer, str1->Length) == 0;
}

// Update indexOf to use your custom function
int indexOf(ArrayList* list, UNICODE_STRING data) {
    for (int index = 0; index < list->size; index++) {
        if (AreUnicodeStringsEqual(&data, &list->elements[index].data)) {
            return index;
        }
    }
    return -1;
}

Quick Tips #

• Always pass pointers to UNICODE_STRING structs to comparison functions (using &)—this is more efficient and aligns with standard string comparison patterns.
• For case-insensitive checks in a custom function, swap memcmp with wcsnicmp (just remember to convert the byte length to character count first).

内容的提问来源于stack exchange，提问作者user9628077