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Better String Library Porting Guide

by Paul Hsieh

The bstring library is an attempt to provide improved string processing functionality to the C and C++ language. At the heart of the bstring library is the management of bstrings which are a significant improvement over '\0' terminated char buffers. See the accompanying documenation for more information.

Identifying the Compiler

Bstrlib has been tested on the following compilers:

  • GNU C/C++
  • Microsoft Visual C++
  • Watcom C/C++ (32 bit flat)
  • Intel's C/C++ compiler (on Windows)
  • The GNU C/C++ compiler (on Windows/Linux on x86 and PPC64)
  • Borland C++
  • Turbo C

There are slight differences in these compilers which requires slight differences in the implementation of Bstrlib. These are accomodated in the same sources using #ifdef/#if defined on compiler specific macros. To port Bstrlib to a new compiler not listed above, it is recommended that the same strategy be followed. If you are unaware of the compiler specific identifying preprocessor macro for your compiler you might find it here.

Note: Intel C/C++ on Windows sets the Microsoft identifier: _MSC_VER

16-bit vs. 32-bit vs. 64-bit Systems

Bstrlib has been architected to deal with strings of length between 0 and INT_MAX (inclusive). Since the values of int are never higher than size_t there will be no issue here. Note that on most 64-bit systems int is 32-bit.

Dependency on The C-Library

Bstrlib uses the functions memcpy, memmove, malloc, realloc, free and vsnprintf. Many free standing C compiler implementations that have a mode in which the C library is not available will typically not include these functions which will make porting Bstrlib to it onerous. Bstrlib is not designed for such bare bones compiler environments. This usually includes compilers that target ROM environments.

Porting Issues

Bstrlib has been written completely in ANSI/ISO C and ISO C++, however, there are still a few porting issues. These are described below.

Weak C++ Compiler

C++ is a much more complicated language to implement than C. This has lead to varying quality of compiler implementations. The weaknesses isolated in the initial ports are inclusion of the Standard Template Library, std::iostream and exception handling. By default it is assumed that the C++ compiler supports all of these things correctly. If your compiler does not support one or more of these define the corresponding macro:

BSTRLIB_CANNOT_USE_STL
BSTRLIB_CANNOT_USE_IOSTREAM
BSTRLIB_DOESNT_THROW_EXCEPTIONS

The compiler specific detected macro should be defined at the top of bstrwrap.h in the Configuration defines section. Note that these disabling macros can be overrided with the associated enabling macro if a subsequent version of the compiler gains support. (For example, its possible to rig up STLport to provide STL support for WATCOM C/C++, so -DBSTRLIB_CAN_USE_STL can be passed in as a compiler option.)

Platform Specific Files

The makefiles for the examples are basically setup of for particular environments for each platform. In general these makefiles are not portable and should be constructed as necessary from scratch for each platform.

Testing a port

To test that a port compiles correctly do the following:

  1. Run make check and ensure that no errors are reported.
  2. Run make memcheck and ensure that no errors are reported.

The builds must have zero errors and zero warnings. The result of execution should be essentially identical on each platform.

Performance

Different CPU and compilers have different capabilities in terms of performance. It is possible for Bstrlib to assume performance characteristics that a platform doesn't have (since it was primarily developed on just one platform). The goal of Bstrlib is to provide very good performance on all platforms regardless of this but without resorting to extreme measures (such as using assembly language, or non-portable intrinsics or library extensions).

There are two performance benchmarks that can be found in the example directory. They are: cbench.c and cppbench.cpp. These are variations and expansions of a benchmark for another string library. They don't cover all string functionality, but do include the most basic functions which will be common in most string manipulation kernels.

Feedback

Please send email to the primary author if you find any issues.