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Download Programming with lcc
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120 C programming with lcc-win32 the same as another random piece of memory, a catastrophe in most cases. You write to a variable and without you knowing it, you are writing to another variable at the same time, destroying all data stored there. More easy to find, since more or less it always provokes a trap, the dangling pointer problem can at any moment become the dreaded show stopper bug that crashes the whole program and makes the user of your program loose all the data he/she was working with. I would be delighted to tell you how to avoid those bugs, but after more than 10 years working with the C language, I must confess to you that memory management bugs still plague my programs, as they plague all other C programmers.68 The basic problem is that the human mind doesn’t work like a machine, and here we are asking people (i.e. programmers) to be like machines and keep book exactly of all the many small pieces of RAM a program uses during its lifetime without ever making a mistake. But there is a solution that I have implemented in lcc-win32. Lcc-win32 comes with an automatic memory manager (also called garbage collector in the literature) written by Hans Boehm. This automatic memory manager will do what you should do but do not want to do: take care of all the pieces of RAM for you. Using the automatic memory manager you just allocate memory with GC_malloc instead of allocating it with malloc. The signature (i.e. the result type and type of arguments) is the same as malloc, so by just replacing all malloc by GC_malloc in your program you can benefit of the automatic memory manager without writing any new line of code. The memory manager works by inspecting regularly your whole heap and stack address space, and checking if there is anywhere a reference to the memory it manages. If it doesn’t find any references to a piece of memory it will mark that memory as free and recycle it. It is a very simple schema, taken to almost perfection by several years of work from the part of the authors. To use the memory manager you should add the gc.lib library to your link statement or indicate that library in the IDE in the linker configuration tab. 1.27.1 Functions for memory allocation malloc Returns a pointer to a newly allocated memory block free Releases a memory block calloc Returns a pointer to a newly allocated zero-filled memory block. realloc Resizes a memory block preserving its contents. alloca Allocate a memory block in the stack that is automatically destroyed when the function where the allocation is requested exits. _msize Returns the size of a block _expand Increases the size of a block without moving it. GC_malloc Allocates a memory block managed by the memory manager. 1.27.2 Memory layout under windows69 A 32 bit address can be used to address up to 4GB of RAM. From this potential address space, windows reserves for the system 2GB, leaving the other 2GB for each application. These 68. This discussion is based upon the article of Randy Kath, published in MSDN.
