Static vs Dynamic Linking: Advantages and Disadvantages
Static vs. Dynamic Linking
A static library is bound at compile time, unlike dynamic linking, which occurs at runtime. The advantage of static linking is that the program doesn’t depend on external libraries, simplifying distribution.
Linking allows dividing a program into modules, assembled separately and linked later, either statically or dynamically. Static linking results in an executable file with all symbols and modules included.
Dynamic Linking
A dynamic link links a code library while a program is running, unlike static linking during compilation. This makes the program lighter and avoids code duplication. For example, multiple programs can use the same library without needing separate copies.
Dynamic link libraries (DLLs) or shared libraries are typically in OS-specific directories. The OS knows where to find them when a program needs them. This can cause dependency issues, especially with different library versions.
Many programs have procedures rarely called. Dynamic linking allows linking each procedure when called after installation.
Static and Dynamic Libraries
A static library is “copied” into your program during compilation. After creating the executable, the library is no longer needed for that program. Only the necessary parts of the library are copied. For example, if a library has two functions and your program only calls one, only that function is copied.
A dynamic library isn’t copied during compilation. When the executable runs, it accesses the library each time it needs something from it. Deleting the library will cause the program to fail.
What are the advantages and disadvantages of each type of library?
- Programs compiled with static libraries are larger.
- Programs compiled with static libraries can be run on other computers without needing the libraries.
- Programs compiled with static libraries are generally faster.
- Changes to a static library don’t affect the executable. Changes to a dynamic library do affect executables. This is advantageous for bug fixes but inconvenient if changes require executable modifications.
Dynamic Link Libraries (DLLs)
DLLs can be seen as an evolution of static libraries, containing functionality or resources used by other applications. They offer several advantages:
- Reduce executable file size: Software can be stored in libraries, improving modularization.
- Shared among applications: Generic code can be used by multiple applications (e.g., MFC).
- Facilitate memory management: Dynamic loading allows the OS to optimize performance. Shared libraries only require one copy in memory.
- Provide flexible responses to change: Performance improvements or bug fixes can be distributed as new library versions, benefiting all applications using the library.