Struct View

Struct View applies a structure defined in a .yupat file to the current cursor position and lets you inspect binary data field by field.

How to Open It

1. Open the file you want to inspect in YuHex.
2. Open the Struct View window from the menu.
3. Click Open... in Struct View and select a .yupat file.
4. The structure is applied relative to the current cursor position in the hex dump area.

Writing .yupat Files

A .yupat file is a C-style structure definition file with a small set of YuHex-specific directives.

Basic Rules

• UTF-8 is recommended.
• Both // ... and /* ... */ comments are supported.
• Use @entry to specify the root structure.
• If the file defines only one structure, @entry can be omitted.

Common Directives

All Directives

Supported Declarations

• struct name { ... };
• typedef struct tag { ... } TYPE;
• typedef existing_type alias;
• typedef struct tag TYPE; style forward declarations
• Normal members: type name;
• Fixed-size arrays: type name[count];
• Flexible arrays: type name[];
• Pointers: type* name;

Limitations

• union, enum, bit fields, and multi-dimensional arrays are not supported.
• Preprocessor constructs such as #include, #define, and conditional compilation are not supported.
• A flexible array [] can only appear as the last member of a structure.

EBNF-style Grammar

file            = { ws | comment | directive | declaration } ;

directive       = "@entry" ident
                | "@sizeof_short" number
                | "@sizeof_int" number
                | "@sizeof_long" number
                | "@sizeof_long_long" number
                | "@sizeof_float" number
                | "@sizeof_double" number
                | "@pointer_size" number
                | "@member_align" number ;

declaration     = typedef_decl
                | struct_decl
                | forward_decl ;

typedef_decl    = "typedef" type_spec declarator_list ";" ;

struct_decl     = [ "typedef" ] "struct" [ ident ] "{"
                  member_decl* "}" [ ident ] ";" ;

forward_decl    = "typedef" "struct" ident ident ";" ;

member_decl     = type_spec declarator ";" ;

type_spec       = builtin_type
                | ident
                | "struct" ident ;

declarator_list = declarator { "," declarator } ;

declarator      = [ "*" ] ident [ array_suffix ] ;

array_suffix    = "[" number "]"
                | "[" "]" ;

Sample

@member_align 0
@pointer_size 8
@entry sample_record

typedef unsigned char  BYTE;
typedef unsigned short WORD;
typedef struct nested_header nested_header_t;

struct nested_header {
    WORD flags;
    BYTE reserved[2];
};

typedef struct sample_record {
    WORD            magic;
    BYTE            version;
    BYTE            name_length;
    BYTE            name[8];
    nested_header_t header;
    void*           next;
    char            payload[];
} sample_record;

This sample includes all currently supported directives, along with typedef, a forward declaration, normal members, a fixed-size array, a nested structure member, a pointer, and a flexible array member.

The patterns folder in the distribution package includes samples such as tftp_rrq.yupat and zip_local_file.yupat. Editing those files is a good way to get started.

Reading the View

Display Behavior

• Nested structures are expanded only one level under the parent row.
• Parent structure rows show an empty value column.
• The view shows up to 256 rows. If there are more, ... is shown at the end.
• Column widths can be changed by dragging. Double-click a column separator to restore the default width.

Value Display Settings

Use the button on the right side of the Value header to change how values are shown.

ASCII string display follows these rules.

• If \0 is found, the string is shown up to that point.
• If a non-ASCII or control character appears, the string is shown up to that point and ... is appended.
• If the data cannot be interpreted as a string from the first byte, the display falls back to hex bytes.

Buttons

Error Display

• If the definition file contains an error, Struct View shows the error message inside the window.
• Error messages include the line number, column number, source line, and caret position.
• The error text area supports text selection and copy.

Notes

• Struct View interprets data from the current cursor position. Move the cursor to the location you want to inspect before opening a definition file.
• Struct View does not apply semantic protocol-specific interpretation by itself. Change the value display mode as needed when checking raw data.

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