FileTell

    }
    
    i64 FileTell(File *f) {
        return FileSeek(f, 0, FILE_SEEK_CUR);
    }

        ok              = ok && (FileWrite(&f, "x", 1) == -1);
        ok              = ok && (FileSeek(&f, 0, FILE_SEEK_SET) == -1);
        ok              = ok && (FileTell(&f) == -1);
    
        FileRemove(&path);

    // observable values.
    bool test_write_seek_read_roundtrip(void) {
        WriteFmt("Testing FileWrite/FileSeek/FileTell/FileRead round-trip\n");
    
        DefaultAllocator alloc      = DefaultAllocatorInit();

    
        // After writing 8 bytes the cursor is at offset 8.
        ok = ok && (FileTell(&f) == 8);
    
        // Seek to absolute offset 2 and confirm Tell agrees.

        // Seek to absolute offset 2 and confirm Tell agrees.
        ok = ok && (FileSeek(&f, 2, FILE_SEEK_SET) == 2);
        ok = ok && (FileTell(&f) == 2);
    
        char got[4] = {0};

    
        // Cursor advanced by the 4 read bytes (2 -> 6).
        ok = ok && (FileTell(&f) == 6);
    
        // Seek to end yields the file length.

        ok = ok && (v == 42);
        // Seekable branch advances to exactly the consumed bytes ("42").
        ok = ok && (FileTell(&f) == 2);
    
        m4_cleanup(&f, &path);

        FReadFmt(&f, "{}", v);
        ok = ok && (v == 53);
        ok = ok && (FileTell(&f) == 2);
    
        m4_cleanup(&f, &path);

        FReadFmt(&f, "{}", v);
        ok = ok && (v == 1234);         // untouched
        ok = ok && (FileTell(&f) == 0); // no advance
    
        m4_cleanup(&f, &path);