.LIB

Introduction

On Windows, a .lib file is a library for the linker, made by the tools in Microsoft Visual Studio and by compatible ones such as LLVM. It comes in two kinds that share one format. A static library holds COFF object files, and the linker copies the ones a program needs into it. An import library holds no code: it tells the linker which functions a DLL exports, so that a program can call them and Windows can load the DLL when the program starts.

The format is a variant of the Unix ar archive. Libraries from 16-bit DOS and Windows compilers also use .lib, but hold OMF object files in a different library format that starts with the byte 0xF0.

Structure

The file starts with !<arch>\n, followed by members, each with a 60-byte text header as in a Unix archive. The first two members are both named /: the first linker member, an index of public symbols in big-endian order kept for compatibility, and the second linker member, a sorted little-endian index that Microsoft’s linker uses. A member named // holds long member names. The remaining members are the object files.

In an import library, each member is usually a short import record instead of a full object file. It starts with the 16-bit values 0 and 0xFFFF, then gives the machine type, the name or ordinal of the imported function, and the DLL’s name.

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