检查程序是否将stderr重定向到stdout

Question

From within a C++ program, is it possible to check whether stderr is redirected into stdout or vice versa? Basically I want to know if those two file descriptors point to the same place. Platform-specific solutions using native APIs are OK.

Answer 1

Linux，也可能是其他unix-like：fstat fds和比较dev：ino对。

Answer 2

for windows 7 and later console handles - this is real file handles (on XP this is not true, about vista - not remember). we can got this 2 handles by call GetStdHandle with STD_OUTPUT_HANDLE and STD_ERROR_HANDLE. but then need somehow compare files by handle. this not equal direct compare handles values - because 2 different handles can point to same file. even if we got pointer to FILE_OBJECT from handle (this possible from user mode) - two different FILE_OBJECTs can point to same file (if we speak about filesystem files). so best way here i think - got names of both files - and compare - are they equal. this can be done by ZwQueryObject . code can be like this

NTSTATUS QueryName(HANDLE hFile, PUNICODE_STRING Name)
{
    union {
        PVOID buf;
        POBJECT_NAME_INFORMATION poni;
    };

    static volatile UCHAR guz;
    PVOID stack = alloca(guz);

    ULONG cb = 0, rcb = 512;
    NTSTATUS status;

    do 
    {
        if (cb < rcb)
        {
            cb = RtlPointerToOffset(buf = alloca(rcb - cb), stack);
        }

        if (0 <= (status = ZwQueryObject(hFile, ObjectNameInformation, buf, cb, &rcb)))
        {
            return RtlDuplicateUnicodeString(0, &poni->Name, Name);
        }

    } while (status == STATUS_BUFFER_TOO_SMALL || status == STATUS_BUFFER_OVERFLOW);

    return status;
}

NTSTATUS AreFilesTheSame(HANDLE h1, HANDLE h2, PBOOL pb)
{
    if (h1 == h2)
    {
        *pb = TRUE;
        return STATUS_SUCCESS;
    }

    if (!h1 || !h2)
    {
        *pb = FALSE;
        return STATUS_SUCCESS;
    }

    UNICODE_STRING name1, name2;
    NTSTATUS status;

    if (0 <= (status = QueryName(h1, &name1)))
    {
        if (0 <= (status = QueryName(h2, &name2)))
        {
            *pb = RtlEqualUnicodeString(&name1, &name2, TRUE);
            RtlFreeUnicodeString(&name2);
        }
        RtlFreeUnicodeString(&name1);
    }

    return status;
}

BOOL b;
AreFilesTheSame(GetStdHandle(STD_OUTPUT_HANDLE), GetStdHandle(STD_ERROR_HANDLE), &b);

but for xp this will be not work