Advantages and disadvantages of dynamic link libraries

Introduced:


DLL is a dynamic link library file, also known as an "application extension", which is a software file type. In Windows, many applications are not a complete executable, and they are split into relatively independent, dynamic-link libraries, DLL files, placed in the system. When we execute a program, the corresponding DLL file is called. An application can use multiple DLL files, and a DLL file may also be used by different applications, such that DLL files are called shared DLL files. [1]



Significance:


DLL files are stored in a variety of program functions (sub-procedures) implementation process, when the program needs to call the function to load the DLL, and then get the address of the function, and finally make the call. The advantage of using DLL files is that the program does not need to load all the code at the beginning of the run, but only when a function is needed by the program to remove it from the DLL. In addition, using DLL files can also reduce the volume of your program.



Advantages:

(1) Save more memory and reduce page switching;

(2) DLL file and EXE file independent, as long as the output interface is unchanged (that is, the name, parameters, return value type and calling convention unchanged), the replacement DLL file will not have any impact on the EXE file, thus greatly improving the maintainability and extensibility;

(3) programs written in different programming languages can call the same DLL function just according to the function calling convention;

(4) Suitable for large-scale software development, make the development process independent, the coupling degree is small, facilitates the development and the test between different developer and the development organization.

(5) Save disk space: When an application uses dynamic linking, multiple applications can share a single copy of the DLL on disk. In contrast, when an application uses a static-link library, each application links the library code to the executable image as a separate copy.

Disadvantages:

An application that uses a dynamic-link library is not self-contained, and it relies on a DLL module to exist, and if you use dynamic linking at load time, the program starts to discover that the DLL does not exist, and the system terminates the program and gives an error message. While using runtime dynamic linking, the system does not terminate, but because the exported function in the DLL is not available, the program fails to load, and the speed is slower than the static link. When a module is updated, if the new module is incompatible with the old module, then the software that needs the module to run will die.

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Reference:

Http://baike.baidu.com/view/230750.htm
http://blog.csdn.net/left_la/article/details/12098545
Http://book.51cto.com/art/201008/216649.htm

Advantages and disadvantages of dynamic link libraries

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