Portability of WSTP Programs
The Wolfram Language side of a Wolfram Symbolic Transfer Protocol (WSTP) connection is set up to work exactly the same on all computer systems. But inevitably there are differences between external programs on different computer systems.
For a start, different computer systems almost always require different executable binaries. When you call Install["prog"], therefore, you must be sure that prog corresponds to a program that can be executed on your particular computer system.
|Install["file"]||try to execute file directly|
|Install["file",LinkProtocol->"type"]||use the specified protocol for low‐level data transport|
|$SystemID||identify the type of computer system being used|
|Install["dir"]||try to execute a file with a name of the form dir/$SystemID/dir|
The Wolfram Language follows the convention that if prog is an ordinary file, then Install["prog"] will just try to execute it. But if prog is a directory, then the Wolfram Language will look for a subdirectory of that directory whose name agrees with the current value of $SystemID and will then try to execute a file named prog within that subdirectory.
|mcc -o prog …||put compiled code in the file prog in the current directory|
|mcc -xo prog …||put compiled code in prog/$SystemID/prog|
Even though the executable binary of an external program is inevitably different on different computer systems, it can still be the case that the source code in a language such as C from which this binary is obtained can be essentially the same.
For a start, you should never make use of extra features of the C language or C runtime libraries that happen to be provided on a particular system, but are not part of standard C. In addition, you should try to avoid dealing with segmented or otherwise special memory models.
The include file wstp.h contains standard C prototypes for all the functions in the WSTP library.
|WSPutInteger32()||WSGetInteger32()||integer corresponding to C type int, that is, 32 bits|
|WSPutInteger16()||WSGetInteger16()||integer of type short, that is, 16 bits|
|WSPutReall64()||WSGetReal64()||IEEE double-precision real number, corresponding to the C-language type double|
|WSPutReal32()||WSGetReal32()||IEEE single‐precision real number, corresponding to the C-language type float|
|WSPutReal128()||WSGetReal128()||IEEE quad‐precision real number|
If your programs correctly match the argument types for the WSTP library functions, you do not have to worry about C type differences between computer systems. WSTP automatically converts the C types to the appropriate sizes for each platform. WSTP also swaps bytes as needed to correctly transfer numbers across platforms and it converts between floating-point number formats with the smallest possible loss of precision.
|WSPutString(stdlink,char*s)||put a null-terminated C character string|
|WSPutUnicodeString(stdlink,unsigned short*s,int n)|
|put a string encoded in terms of 16‐bit UCS-2 Unicode characters|
|WSPutByteString(stdlink,unsigned char*s,int n)|
|put a string containing only 8‐bit character codes|
|WSPutUTF8String(stdlink, const unsigned char*s,int n)||put a string of UTF-8 encoded Unicode characters|
|WSPutUTF16String(stdlink, const unsigned short*s,int n)||put a string of UTF-16 encoded Unicode characters|
|WSPutUTF32String(stdlink, const unsigned int*s,int n)||put a string of UTF-32 encoded Unicode characters|
|WSGetString(stdlink,char**s)||get a null-terminated C character string|
|get a string encoded in terms of 16‐bit UCS-2 Unicode characters|
|WSGetByteString(stdlink,unsigned char**s,long*n,long spec)|
|get a string containing only 8‐bit character codes, using spec as the code for all 16‐bit characters|
|WSGetUTF8String(stdlink, const unsigned char**s,int*m,int*n)||get a string of UTF-8 encoded Unicode characters|
|WSGetUTF16String(stdlink, const unsigned short**s,int*m,int*n)||get a string of UTF-16 encoded Unicode characters|
|WSGetUTF32String(stdlink, const unsigned int**s,int*n)||get a string of UTF-32 encoded Unicode characters|
In simple C programs, it is typical to use strings that contain only ordinary ASCII characters. But in the Wolfram Language, it is possible to have strings containing all sorts of special characters. These characters are specified within the Wolfram Language using Unicode character codes, as discussed in "Raw Character Encodings".
C language char* strings typically use only 8 bits to store the code for each character. UCS-2 encoded strings, however, require 16 bits. As a result, the functions WSPutUnicodeString() and WSGetUnicodeString() work with arrays of unsignedshort integers. The same is true of UTF-16 encoded strings and the corresponding functions WSPutUTF16String() and WSGetUTF16String().
If you know that your program will not have to handle special characters, then you may find it convenient to use WSPutByteString() and WSGetByteString(). These functions represent all characters directly using 8‐bit character codes. If a special character is sent from the Wolfram Language, then it will be converted by WSGetByteString() to a fixed code that you specify.
Computer systems and compilers that have C runtime libraries based on the Unix model allow WSTP programs to have a main program of the form main(argc,argv) that simply calls WSMain(argc,argv).
Some computer systems or compilers may, however, require main programs of a different form. You should realize that you can do whatever initialization you want inside main() before calling WSMain(). Once you have called WSMain(), however, your program will effectively go into an infinite loop, responding to requests from the Wolfram Language until the link to it is closed.