general / lpc

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  • What is LPC?

LPC is the language in which MudOS (and LPmud) objects are written. LPC stands for Lars Pensj| C. As one might surmise from the name, LPC is based on the syntax of C. LPC provides the C while loop, for loop, if statement, switch statement, a variant of sscanf, and integer data type, (LPC also provides other data types not in C such as the object and the mapping). LPC uses C’s syntax for defining and calling functions and for declaring variables. Note that LPC’s version of the string datatype is much different from that provided by C. See the LPC tutorial on syntax and language constructs for more information.

Here are some differences between LPC and C:

There is no need for a function named “main” in LPC objects (although there is one called “create”).

The efuns (or system calls) provided by the gamedriver are different than those typically found in the C library (libc.a).

There is no malloc(). However, there is an allocate(int value) efun that lets space be allocated for arrays. Note that the argument to ‘allocate’ is not in units of bytes, but rather in units of elements.

Memory is never explicitly deallocated. The gamedriver keeps track of how many times a given piece of data has been referenced. When the reference count goes to zero (when no object has a copy of that variable), then the space used by the variable is reclaimed (garbage collected).

The string data type in LPC is closer to that provided by BASIC than that provided by C. Strings are not declared as arrays of characters but rather as a basic intrinsic type. Strings may be concatenated using the ‘+’ operator.

For example, the LPC statements:

string ack;

ack = foo + bar;

are equivalent to the C statements:

char *ack;

ack = (char _)malloc(strlen(foo) + 1); strcpy(ack,foo); ack = (char _)realloc(strlen(ack) + strlen(bar) + 1); strcat(ack,bar);

LPC is an interpreted language (however it is compiled into an internal compact tokenized form before being interpreted).

LPC has no structures or unions. In fact, the -> operator is used to indicate a call to another object. The mapping datatype can serve as an effective substitute for structures in some situations.

sscanf does not work in the same way as in C. arguments to sscanf need not be pointers (since LPC does not have the explicit pointer data type). Also, sscanf(arg,”%s %s”,str1,str2) does not operate as the C programmer would expect. In C, the first word of arg would be copied into str1 and the second word of arg into str2. In LPC, the first word is copied into str1 and the remainder of arg is copied into str2.