SystemTimeToVariantTime发生缓冲区溢出，求排查（附日期转换函数代码）

Let’s break down what’s causing that buffer overflow and fix your code step by step:

Key Issues in Your Original Code #

• Mismatched Format Specifiers: Every member of SYSTEMTIME is a WORD (an alias for unsigned short), but you’re using %d (the format specifier for 4-byte int) with sscanf_s. When the function tries to write a full int value into a 2-byte WORD variable, it overruns the SYSTEMTIME structure’s memory. This corruption triggers the buffer overflow when SystemTimeToVariantTime tries to read the damaged data.
• Risky Wide-to-Narrow Conversion: Using ConvertWstringToCharStar introduces unnecessary complexity—if this function doesn’t allocate memory correctly or returns a pointer to temporary data, you could end up parsing garbage values that worsen the overflow.
• No Error Checking: You aren’t verifying if sscanf_s successfully parsed all date fields, so invalid input could lead to partial writes that corrupt the SYSTEMTIME structure.

Fixed Code Implementation #

Here’s a revised, safer version of your function:

#include <wchar.h>
#include <stdexcept>

void ConvertDateIntoSystemFormat(const std::wstring& dateModified, DATE& date) {
    // Initialize SYSTEMTIME to zero with C++ initializer list (cleaner than memset)
    SYSTEMTIME systemTime = {0};

    // Use swscanf_s to handle wide strings directly—no need for conversion
    int parsedFieldCount = swscanf_s(
        dateModified.c_str(),
        L"%hu-%hu-%huT%hu:%hu:%hu.%huZ",
        &systemTime.wYear,
        &systemTime.wMonth,
        &systemTime.wDay,
        &systemTime.wHour,
        &systemTime.wMinute,
        &systemTime.wSecond,
        &systemTime.wMilliseconds
    );

    // Ensure all 7 date/time fields were parsed correctly
    if (parsedFieldCount != 7) {
        throw std::invalid_argument("Input doesn't match ISO 8601 format (YYYY-MM-DDTHH:MM:SS.sssZ)");
    }

    // Validate the conversion to DATE type
    if (!SystemTimeToVariantTime(&systemTime, &date)) {
        throw std::runtime_error("Failed to convert system time to DATE variant");
    }
}

What Changed & Why #

1. Switched to swscanf_s: This wide-character scan function works directly with std::wstring (via c_str()), eliminating the need for risky wide-to-narrow string conversion.
2. Corrected Format Specifiers: %hu is the proper format for unsigned short (aka WORD), so we no longer write beyond the bounds of each SYSTEMTIME member.
3. Safer Initialization: Using SYSTEMTIME systemTime = {0}; is more idiomatic C++ and ensures all structure members start at zero without relying on memset.
4. Added Error Checking: We verify that all date fields are parsed, and that the final conversion to DATE succeeds. This catches invalid input before it causes memory issues.
5. Const Reference Parameter: Changing dateModified to a const std::wstring& avoids unnecessary string copies and guarantees we don’t modify the input.

Bonus: Optional Validation #

For extra robustness, you can add checks for valid date values (e.g., months 1-12, days matching the month) before calling SystemTimeToVariantTime—this prevents invalid SYSTEMTIME values from causing unexpected behavior.

内容的提问来源于stack exchange，提问作者beasone