When it comes to creating C/C++ DLLs (Dynamic Link Libraries), one of the most important factors to consider is the size of the .def (definition) files. These files contain the definitions of the functions and variables that are exported from the DLL, and are essential for its proper functioning. However, if not optimized properly, .def files can significantly increase the size of the DLL, causing performance issues and making it difficult to manage. In this article, we will discuss some tips for optimizing .def files for C/C++ DLLs.
1. Use Forward Declarations
One of the simplest ways to reduce the size of .def files is by using forward declarations. Instead of including the entire header file in the .def file, only declare the functions and variables that are needed. This will not only reduce the size of the .def file but also make it easier to manage, as you won't have to update the .def file every time the header file changes.
2. Use Module Definitions
Module definitions are a great way to group related functions and variables in a single module. This not only makes it easier to manage the .def file but also reduces its size by eliminating duplicate entries. To use module definitions, simply add the keyword "module" before the module name, followed by a colon. Then list all the functions and variables within that module, separated by commas.
3. Use the "NoDefaultLib" Option
The "NoDefaultLib" option tells the linker to ignore the default library files when linking the DLL. This means that only the functions and variables specified in the .def file will be exported, reducing the size of the DLL significantly. To use this option, add the keyword "nodefaultlib" after the "EXPORTS" keyword in the .def file.
4. Use the "Noname" Option
The "Noname" option tells the linker to use ordinal numbers instead of names for the exported functions and variables. This can significantly reduce the size of the .def file, as ordinal numbers are shorter than function names. To use this option, add the keyword "noname" after the "EXPORTS" keyword in the .def file.
5. Use the "Ansi" Option
The "Ansi" option tells the linker to use ANSI strings instead of Unicode strings for the exported functions and variables. This can significantly reduce the size of the .def file, as ANSI strings are shorter than Unicode strings. To use this option, add the keyword "ansi" after the "EXPORTS" keyword in the .def file.
6. Use the "NoEntry" Option
The "NoEntry" option tells the linker not to generate an entry point for the DLL. This is useful if you are creating a DLL that will only be used by other DLLs and not by applications directly. By not generating an entry point, you can reduce the size of the DLL even further. To use this option, add the keyword "noentry" after the "EXPORTS" keyword in the .def file.
7. Use the "OptRef" Option
The "OptRef" option tells the linker to optimize the .def file by removing unreferenced functions and variables. This can significantly reduce the size of the .def file, especially if you have a large number of functions and variables. To use this option, add the keyword "optref" after the "EXPORTS" keyword in the .def file
