This project is obsolete. When uSTL was created back in 2003, the C++ standard library implementation was implemented poorly, without any concern for code size, template bloat, or memory footprint. This library was then intended to remedy those problems and succeeded reasonably well, providing savings of several kb of code size per container, several megabytes of savings in memory footprint, and a variety of small space-saving and performance improvements. Today the official standard library implementation has improved drastically, owing to improvements in the C++ standard itself, as well as laudable optimization efforts by gcc developers. Furthermore, due to proliferation of C++-using applications, memory footprint reductions from using uSTL are no longer possible. Compared to the official standard library implementation, uSTL provides very little advantage, and many drawbacks due to the design tradeoffs and limitations that made the space savings originally possible. Therefore I strongly recommend that uSTL no longer be used in any new projects. I shall continue to maintain the library for existing users, if any, but would likewise recommend that you too use the official standard library instead.



The only dependency is a C++ compiler, gcc 5 or clang 3.6. clang does not optimize for size as well as gcc, producing binaries larger by about 15%, so its use is not recommended.

The latest version of uSTL can always be downloaded from its GitHub release page. If you like living dangerously, you can pull the working branch directly from The mainline source should build on any unix-based system, including Linux, BSD, MacOS, SunOS, and Solaris. Windows-based systems and embedded platforms, are not, and will not be supported by the mainline. Unpack and:

./configure && make install

./configure --help lists available build options. You might want to specify a different installation prefix with --prefix=/usr; the default destination is /usr/local. You may want to also use --with-forced-inline. Unless you are compiling a package for distribution, --with-native should be enabled to tune the output for your processor. If you are the type to edit configuration manually, it's in and config.h. When it's built, you can run the included tests with make check. Here's a simple hello world application:

#include <ustl.h>
using namespace ustl;

int main (void)
    cout << "Hello world!" << endl;
    return EXIT_SUCCESS;

Compile the sources with g++, but link the executable with gcc. g++ will link with -lstdc++ by default, but to use uSTL you need to link with -lustl -lsupc++ instead. The right way to get this list of libraries is to use pkg-config --libs ustl. The pkg-config description file for uSTL is installed if you have pkg-config on your system.

To build uSTL with debug info, run make debug=1 install. This will build and install libustl_d.a. Unfortunately, there is no standard for naming a separate library with debug info. When developing you want to have both for each of your project's dependencies, so you could quickly switch between building a debug version for troubleshooting and an optimized version for release or local use. For this purpose I came up with this dual file system. The derived project links with the pkg-config-provided libs, but the makefile also has a debug section for rewriting the name:

ifdef debug
    cxxflags	:= -O0 -ggdb3
    ldflags	:= -g -rdynamic
    libs	:= $(subst lustl,lustl_d,${libs})
    cxxflags	:= -Os -g0 -DNDEBUG=1
    ldflags	:= -s

This way you can build a debug version of your project with make debug=1, automatically linking with debug versions of each dependent library. A bit unusual, but it works.

Containers and Iterators

STL containers provide a generic abstraction to arrays, linked lists, and other methods of memory allocation. They offer the advantages of type-safety, the peace of mind that comes from never having to malloc anything again, and a standard access API called iterators. Each container's API is equivalent to that of a simple array, with iterators being the equivalent of pointers into the array. The uniform access API allows creation of standardized algorithms, discussed futher down, that work on any container. Here are some examples of using vector, the container representing a simple array:

vector<int> v;
v.push_back (1);
v.emplace_back (2);
v[1] = 0;
v.erase (v.begin() + 1);
v.insert (v.begin(), 4);
v.resize (15);

As you can see, a vector is basically the same thing as the arrays you use now, except that it is resizable. The function names ought to be self-explanatory with the exception of the addressing arguments. You can do index addressing and get free bounds checking with asserts. Incidentally, I highly recommend you work with a debug build when writing code; uSTL is chock full of various asserts checking for error conditions. In the optimized build, most such errors will be silently ignored where possible and will cause crashes where not. That is so because they are programmer errors, existing because you have a bug in your code, not because the user did something wrong, or because of some system failure. Programmer errors assert. User or system errors throw exceptions.

Vectors are addressed with iterators, which are just like pointers (and usually are). Calling begin() gives you the pointer to the first element, calling end() gives you the pointer to the end of the last element. No, not the last element, the end of it, or, more accurately, the end of the array. It's that way so you can keep incrementing an iterator until it is equal to the end() value, at which point you know you have processed all the elements in the list. This brings me to demonstrate how you ought to do that:

foreach (auto, i, v)
    if (*i < 5 || *i > 10)
	*i = 99;

Although the foreach macro is a uSTL-only extension, it is a one-liner you can easily copy out of uutility.h if you ever want to switch back to regular STL. It is a great way to ensure you don't forget to increment the counter or run past the end of the vector. The only catch to be aware of, when inside an iterator loop, is that if you modify the container, by adding or removing entries, you have to update the iterator, since the container memory storage may have moved when resized. So, for example, if you wish to remove certain types of elements, you'd need to do use an index loop or something like:

foreach (auto, i, employees)
    if (i->m_Salary > 50000 || i->m_Performance < 100)
	--(i = employees.erase (i));

This is pretty much all there is to say about containers. Create them, use them, resize them, that's what they are for. There are other container types, but you will probably not use them much. There's set, which is a perpetually sorted vector, useful when you want to binary_search a large collection. There's map which is an associative container where you can look up entries by key. Its utility goes down drastically when you have complex objects that need to be searched with more than one parameter, in which cast you are better off with vector and foreach.

It is important to mention here that all uSTL containers are built on top of vector, and have the same iterator invalidation semantics. The standard library implementation of non-vector containers uses linked backends, where, for example, inserting into the middle does not invalidate iterators to other elements. If your code depends on this behavior, you can not use uSTL. Linked container backends are very inefficient today because of their poor cache locality, which is the most important factor for performance on modern processors.


Every program uses strings, and STL was kind enough to provide a specification. uSTL deviates a bit from the standard by not implementing wchar strings. There is only one string class, which assumes all your strings will be UTF8-encoded, and provides some additional functionality to make working with those easier. I did that for the same reason I dropped the locale classes; bloat. It is simply too expensive to implement the standard locale classes, as the enormous size of libstdc++ illustrates. If you need them, you can still include them from libstdc++, but it may be just as simple to use the locale support provided by libc through printf, which may be called through format functions in string and ostringstream.

Anyway, back to strings. You can think of the string object as a char vector with some additional operations built-in, like searching, concatenation, etc.

string s ("Hello");
s += ' ';
s += "world?";
s.replace (s.find ('?'), 1, "!");
s[3] = s[s.find_first_of("lxy")];
s[s.rfind('w')] = 'W';
s.format ("A long %zd number of 0x%08lX\n", 345u, 0x12345);
cout << s << endl;

A nonstandard behaviour you may encounter is from linked strings created by the string constructor when given a null-terminated const string. In the above example, the constructor links when given a const string and stays as a const link until the space is added. If you try to write to it, you'll get an assert telling you to use copy_link first to convert the link into a copy. Resizing the linked object automatically does that for you, so most of the time it is transparent. You may also encounter another instance of this if you try getting iterators from such an object. The compiler uses the non-const accessors by default for local objects, so you may need to declare it as a const string if you don't wish to copy_link. Why does uSTL string link instead of copying? To save space and time. All those strings are already in memory, so why waste heap space and processor time to copy them if you just want to read them? I thought it a good tradeoff, considering that it is trasparent for the most common uses.

Other nonstandard extensions include a format function to give you the functionality of sprintf for string objects. Another is the UTF8 stuff. Differing a bit from the standard, size returns the string length in bytes, length in characters. You can iterate by characters instead of bytes with a special utf8 iterator:

for (auto i = s.utf8_begin(); i < s.utf8_end(); ++i)
    DrawChar (*i);

or just copy all the chars into an array and iterate over that:

vector<wchar_t> result (s.length());
copy (s.utf8_begin(), s.utf8_end(), result.begin());

To write wide characters to the string, wchar_t values can be directly given to push_back, insert, append, or assign, in the same way as the char ones.

A few words must be said regarding reading wide characters. The shortest possible rule to follow is "don't!" I have received a few complaints about the fact that all offsets given to and returned by string functions are byte offsets and not character offsets. The problem with modifying or even looking for specific wide characters is that you are not supposed to know what they are. Your strings will be localized into many languages and it is impossible for you to know how the translation will be accomplished. As a result, whenever you are hardcoding a specific character value, or a specific character length (like a three-character extension), you are effectively hardcoding yourself into a locale. The only valid operation on localized strings is parsing it via standard delimiters, treating anything between those delimiters as opaque blocks. For this reason, whenever you think you need to do something at a particular character offset, you should recognize it as a mistake and find the offset by the content that is supposed to be there.

If this philosophy is consistently followed, it becomes clear that actual character boundaries are entirely irrelevant. There are only two exceptions to this: first occurs if you are writing a text editor and want to insert user data at a character position, the second occurs if you are writing a font renderer and want to translate characters to glyphs. In both cases you should make use of the utf8_iterator to find character boundaries and values. Given that these two cases apply to just a handful of people who are involved in implementing user interface frameworks, I believe that the opacity restriction is well justified by the amount of code space it saves for the vast majority of library users.


Algorithms are the other half of STL. They are simply templated common tasks that take iterator arguments, and as a result, work with any container. Most will take an iterator range, like (v.begin(), v.end()), but you can, of course operate on a subset of a container by giving a different one. Because the usual operation is to use the whole container, uSTL provides versions of most algorithms that take container arguments instead of the iterator range. Here are the algorithms you will actually find useful:

copy (v1, v2.begin());		// Copies vector v1 to vector v2.
fill (v, 5);			// Fills v with fives.
copy_n (v1, 5, v2.begin());	// Copies first five elements only.
fill_n (v.begin() + 5, 10, 5);	// Fills elements 5-15 with fives.
sort (v);			// Sorts v.
find (v, 14);			// Finds 14 in v, returning its iterator.
binary_search (v, 13);		// Looks up 13 with binary search in a sorted vector.
lower_bound (v, 13);		// Returns the iterator to where you want to insert 13.
iota (v.begin(), v.end(), 0);	// Puts 0,1,2,3,4,... into v.
reverse (v);			// Reverses all the elements in v.

The rest you can discover for yourself. There are obscure mathematical operations, like inner_product, set operations, heap operations, and many predicate algorithms, taking a function. Predicate algorithms used to be useless before c++11 added support for lambda functions. With c++11 you can use these generic algorithms much easier:

int minValue = 5, maxValue = 10, badBalue = 99;
for_each (v.begin(), v.end(), [=](int& v) {
    if (v < _minValue || v > _maxValue)
	v = _badValue;

And yes, it really does work. Doesn't always generate much bloat either, since the compiler can often see right through all this trickery and expand the for_each into a loop without actually creating the functor object. However, the compiler has a much harder time when you start using containers of complex objects or operating on member variables and member functions. And in general, functional programming should be discouraged. The equivalent imperative version is usually easier to read and it represents the way the processor really works, as well as the way you should be thinking about code. Leave functional to the academics and the overly mathematical. In the real world, we do things step by step.

Memblocks and Memlinks

The STL specification is only about containers and algorithms, the stuff described from here on is totally non-standard.

The major difference between the standart STL implementation and uSTL is that the former has memory management stuff all over the place, while the latter keeps it all together in the memblock class. Normally STL containers are resized by calling new to create more storage and then copying the elements there from the old one. This method wastes space by fragmenting memory, wastes time by copying all the existing data to the new location, and wastes codespace by having to instantiate all the resizing code for each and every container type you have. This method is also absolutely necessary to do this resizing in a perfectly object-safe way. The uSTL way is to manage memory as an opaque, typeless block, and then use the container templates to cast it to an appropriate pointer type.

This works just fine, except for one catch: all objects stored in uSTL containers must be relocatable -- they must not have pointers into themselves. In other implementations, resizing actually creates new objects in the new location and destroys them in the old location. uSTL simply memcpys them there without calling the copy constructor. In other words, the object can not rely on staying at the same address. Most objects really don't care. Note that this is not the same thing as doing a bitwise copy, that you were rightly warned against before! It's a bitwise move that doesn't create a new object, but simply relocates an existing one.

What this one small concession does is allow aggregation of all memory management in one place, namely, the memblock class. All the containers are thus converted mostly into typecasting wrappers that exist to ensure type safety. Look at the assembly code and you'll see mostly calls to memblock's functions. This is precisely the feature that allows reduction in code instantiated by container templates.

However, memblock's usefulness doesn't end there! It can now replace all your dynamically allocated buffers that you use for unstructured data. Need to read a file? Don't use new to allocate memory; use a memblock! It even has a friendly read_file member function for just that purpose. Need to write a file? Use the write_file call! Unless you are working with a database or some really large archive, you should be able to load all your files this way. Imagine, not having to worry about file I/O again! It's much nicer to work with data in memory; you know how long it is, so you know when to stop. You can seek with impunity, and any operations have the cost of a memcpy.

Memblock is derived from memlink, an object for linking to a memory block. Now you get to store a pointer and the size of whatever it points to, but with uSTL you can use a memlink object to keep them together, reducing source clutter and making your code easier to read and maintain. You can link to constant blocks too with cmemlink, from which memlink is derived. Because all three are in a single hierarchy, you never need to care whether you're working on an allocated block or on somebody else's allocated block. Pointers are kept together with block sizes, memory is freed when necessary, and you never have to call new or delete again. Who needs garbage collection? Memblocks give you the same functionality at a fraction of the cost.

Linking is not limited to memlink. You can link memblock objects. You can link string objects. You can even link containers! Now you can use alloca to create a vector on the stack; use the typed_alloca_link(v,int,99) macro. All linked objects will allocate memory and copy the linked data when you increase their size. You can also do it explicitly by calling copy_link. Why link? It's cheaper than copying and easier than keeping track of pointers. For example, here's a line parser:

string buf, line;
buf.read_file ("some_config_file.txt");
for (auto i = 0u; i < buf.size(); i += line.size() + 1) { (buf.iat(i), buf.iat (buf.find ('\n',i)));
    process_line (line);

This way process_line gets a string object instead of a pointer and a size. If you don't rely on the string being null-terminated, which basically means not using libc functions on it, this is all you need. Otherwise buf will have to be writable and you can replace the newline with a null. In either case you are using no extra heap. The overhead of link is negligible in most cases, but if you really want to do this in a tight loop, you can use relink call, which expands completely inline into one or two instructions, avoiding the virtual unlink() call.


The C++ standard library provides global stream objects called cin, cout, and cerr to replace printf and friends for accessing stdin, stdout, and stderr, respectively. uSTL versions work mostly the same as the standard ones (yes, the format call is a uSTL extension). Most calls use snprintf for output and thus use whatever locale libc uses.

cout << "Hello world!" << endl;
cout << 456 << ios::hex << 0x1234 << endl;
cerr.format ("You objects are at 0x%08X\n", &o);

String-writing streams are also available:

ostringstream os;
os << "Writing " << n << " objects somewhere" << endl;
cout << os.str() << endl;

fstream is a file access interface with exception handling for errors:

fstream f;
// C++ standard says that fstream does not throw by default,
f.exceptions (fstream::allbadbits);	// so this enables throwing. ("file.dat", ios::in| ios::out); // throws file_exception (buf, bufSize);			// let's read something (334455);			// go somewhere
f.write (buf2, buf2Size);		// and write something
f.fnctl (FCNTLID(F_SETFL), O_NONBLOCK); // yup, ALL file operations
memlink l = f.mmap (bufSize, offset);	// even mmap
fill (l, 0);
f.msync (l);
f.munmap (l);
f.close();	// also throws file_exception (with filename!)

istream and ostream, which are not really usable by themselves in the standard implementation, are hijacked by uSTL to implement binary data input and output:

const size_t writtenSize =
    Align (stream_size_of(number) +
           stream_size_of(ctr)) + 
    stream_size_of(n) +
memblock buf (writtenSize);
ostream os (buf);
os << number << ctr;
os << n << v;

These operations are all very efficient, approaching a straight memcpy in performance. ostream will not resize the buffer, hence the necessity to estimate the final size. Most stream_size_of calls are computed at compile time and thus produce no code. Because the data is written as is, it is necessary to consider proper data alignment; for example, a 4 byte int can not be written at stream offset 2. Some architectures (Macs) actually crash when doing it; Intel processors just do it slowly. Hence the need to pack the data to a proper "grain". The default align call will pack to the maximum necessary grain, but can be given an argument to change that. In case you're wondering, the reason for all these idiosyncracies is optimization. The smallest and fastest possible code to dump your stuff into a binary file is produced by this method. uSTL defines flow operators to write integral values, strings, and containers, but you can custom-serialize your objects like this:

/// Some class I want to serialize
class CMyClass {
    void	read (istream& is);
		    { is >> _elements >> _someSize >> _someObject; }
    void	write (ostream& os) const;
		    { os << _elements << _someSize << _someObject; }
    size_t	stream_size (void) const {
		    return (stream_size_of (_elements) +
			    stream_size_of (_someSize) +
			    stream_size_of (_someObject));
    vector<int>	_elements;	///< A bunch of elements.
    size_t	_someSize;	///< Some integral value.
    MyObject	_someObject;	///< Some other streamable object.

CMyClass o;
memblock buf (stream_size_of(o));
ostream os (buf);
os << o;
buf.write_file ("output.dat");


One last container I'll mention is array, which is a fixed-size array of identical elements. There is also the older version of this called tuple, with template parameters in reversed order, written for uSTL before C++11 came out with array. These classes are good for graphical objects like points, sizes, rectangles, triangles, etc. tuples have SIMD instruction optimizations, which may or may not be a benefit. Any C-style fixed size-array works better as one of these, since it becomes a standard STL container, which you can use with any algorithm, copy by assignment, initialize in the constructor, etc.

using coord_t = short int;
using Point2d = tuple<2, coord_t>;
using Size2d = tuple<2, coord_t>;
using Rect = array<Point2d, 2>;

Rect r (Point2d (1,2), Point2d (3,4));
r += Size2d (4, 4);
r[1] -= Size2d (1, 1);
for (auto& i : r)
    TransformPoint (i);
Point2d pt (1, 2);
pt += r[0];
pt *= 2;


uSTL implements all the standard exception classes defined by the C++ standard. The exception tree is standalone, but is derived from std::exception when compiling with libstdc++ for ease of catching everything. uSTL exceptions implement some additional useful features. First, they are completely serializable. You can write them as a binary blob into a file, send them over a network, and handle them somewhere else. Each exception will print an informative error message directly to a text stream, reducing your try/catch block to:

try {
} catch (exception& e) {
    cerr << "Error: " << e << endl;
    #ifndef NDEBUG
	cerr << e.backtrace();
} catch (...) {
    cerr << "Unexpected fatal error has occured.\n";

Second, each exception stores a backtrace (callstack) at the time of throwing and can print that backtrace as easily as the above example illustrates. While it is indeed a good practice to design your exceptions so that you should not care where it was thrown from, situations occasionally arise while debugging where knowing the thrower is useful to fix the bug a little faster than otherwise.

Finally, there are additional exception classes for dealing with libc function errors, file errors, and stream classes. system_error can be thrown whenever a libc function fails, immediately telling you what the function call was and the errno description of the failure. file_exception, thrown by fstream operations, also contains the file name, which can be pretty darn useful. stream_bounds_exception is extremely useful in debugging corrupted data, as it tells you exactly where the corruption starts and what you were trying to read there.

Bug reporting

Report bugs through the project issue tracker.