STC - Smart Template Containers for C

News

VERSION 2.X RELEASED: There are two main breaking changes from V1.X.

Now uses a different way to instantiate templated containers, which is incompatible with v1.X.
c_forauto, c_forvar, c_forscope are now renamed to c_auto, c_autovar, and c_autoscope. There is also a c_exitauto macro, which breaks out of an auto-block. The auto name refers to the original meaning of auto keyword in C, namely automatic stack allocated variable, however now it covers automatic resource (de)allocation in general.

The new template instantiation style has multiple advantages, e.g. implementation does not contain long macro definitions for code generation. Also, specfiying template arguments is more user friendly and flexible.

Introduction

A modern, templated, user-friendly, fast, fully type-safe, and customizable container library for C99, with a uniform API across the containers, and is similar to the c++ standard library containers API. For an introduction to templated containers, please read the blog by Ian Fisher on type-safe generic data structures in C.

STC is a compact, header-only library with the all the major "standard" data containers, except for the multimap/set variants. However, there is an example how to create a multimap in the examples folder.

Others:

Highlights

User friendly - Just include the headers and you are good. The API and functionality is very close to c++ STL, and is fully listed in the docs.
Templates - Use #define i_xxx to specify container template arguments. There are templates for element-type, -comparison, -destruction, -cloning, -conversion types, and more.
Unparalleled performance - Some containers are much faster than the c++ STL containers, the rest are about equal in speed.
Fully memory managed - All containers will destruct keys/values via destructor defined as macro parameters before including the container header. Also, shared pointers are supported and can be stored in containers, see csptr.
Fully type safe - Because of templating, it avoids error-prone casting of container types and elements back and forth from the containers.
Uniform, easy-to-learn API - Methods to construct, initialize, iterate and destruct have uniform and intuitive usage across the various containers.
Small footprint - Small source code and generated executables. The executable from the example below with six different containers is 22 kb in size compiled with gcc -Os on linux.
Dual mode compilation - By default it is a simple header-only library with inline and static methods only, but you can easily switch to create a traditional library with shared symbols, without changing existing source files. See the Installation section.
No callback functions - All passed template argument functions/macros are directly called from the implementation, no slow callbacks which requires storage.
Compiles with C++ and C99 - C code can be compiled with C++ (container element types must be POD).
Container prefix and forward declaration - Templated containers may have user defined prefix, e.g. myvec_push_back(). They may also be forward declared without including the full API/implementation. See documentation below.

Performance

Benchmark notes:

The barchart shows average test times over three platforms: Mingw64 10.30, Win-Clang 12, VC19. CPU: Ryzen 7 2700X CPU @4Ghz.
Containers uses value types uint64_t and pairs of uint64_tfor the maps.
Black bars indicates performance variation between various platforms/compilers.
Iterations are repeated 4 times over n elements.
find(): not executed for forward_list, deque, and vector because these c++ containers does not have native find().
deque: insert: n/3 push_front(), n/3 push_back()+pop_front(), n/3 push_back().
map and unordered map: insert: n/2 random numbers, n/2 sequential numbers. erase: n/2 keys in the map, n/2 random keys.

Usage

The usage of the containers is similar to the c++ standard containers in STL, so it should be easy if you are familiar with them. All containers are generic/templated, except for cstr and cbits. No casting is used, so containers are type-safe like templates in c++. A basic usage example:

#define i_val float
#include <stc/cvec.h>

int main(void) {
    cvec_float vec = cvec_float_init();
    cvec_float_push_back(&vec, 10.f);
    cvec_float_push_back(&vec, 20.f);
    cvec_float_push_back(&vec, 30.f);

    c_foreach (i, cvec_float, vec)
        printf(" %g", *i.ref);

    cvec_float_del(&vec);
}

In order to include two cvecs with different element types, include cvec.h twice. For structs, specify a compare function (or none), as < and == operators does not work on them (this enables sorting and searching).

#define i_val struct One
#define i_tag one
#define i_cmp c_no_compare
#include <stc/cvec.h>

#define i_val struct Two
#define i_tag two
#define i_cmp c_no_compare
#include <stc/cvec.h>
...
cvec_one v1 = cvec_one_init();
cvec_two v2 = cvec_two_init();

With six different containers:

#include <stdio.h>
#include <stc/ccommon.h>

struct Point { float x, y; };

int Point_compare(const struct Point* a, const struct Point* b) {
    int cmp = c_default_compare(&a->x, &b->x);
    return cmp ? cmp : c_default_compare(&a->y, &b->y);
}

#define i_key int
#include <stc/cset.h>  // cset_int: unordered set

#define i_tag pnt
#define i_val struct Point
#define i_cmp Point_compare
#include <stc/cvec.h>  // cvec_pnt: vector of struct Point

#define i_val int
#include <stc/cdeq.h>  // cdeq_int: deque of int

#define i_val int
#include <stc/clist.h> // clist_int: singly linked list

#define i_val int
#include <stc/cstack.h>

#define i_key int
#define i_val int
#include <stc/csmap.h> // csmap_int: sorted map int => int

int main(void) {
    // define six containers with automatic call of init and del (destruction after scope exit)
    c_auto (cset_int, set)
    c_auto (cvec_pnt, vec)
    c_auto (cdeq_int, deq)
    c_auto (clist_int, lst)
    c_auto (cstack_int, stk)
    c_auto (csmap_int, map)
    {
        // add some elements to each container
        c_apply(cset_int, insert, &set, {10, 20, 30});
        c_apply(cvec_pnt, push_back, &vec, { {10, 1}, {20, 2}, {30, 3} });
        c_apply(cdeq_int, push_back, &deq, {10, 20, 30});
        c_apply(clist_int, push_back, &lst, {10, 20, 30});
        c_apply(cstack_int, push, &stk, {10, 20, 30});
        c_apply_pair(csmap_int, insert, &map, { {20, 2}, {10, 1}, {30, 3} });

        // add one more element to each container
        cset_int_insert(&set, 40);
        cvec_pnt_push_back(&vec, (struct Point) {40, 4});
        cdeq_int_push_front(&deq, 5);
        clist_int_push_front(&lst, 5);
        cstack_int_push(&stk, 40);
        csmap_int_insert(&map, 40, 4);

        // find an element in each container
        cset_int_iter_t i1 = cset_int_find(&set, 20);
        cvec_pnt_iter_t i2 = cvec_pnt_find(&vec, (struct Point) {20, 2});
        cdeq_int_iter_t i3 = cdeq_int_find(&deq, 20);
        clist_int_iter_t i4 = clist_int_find(&lst, 20);
        csmap_int_iter_t i5 = csmap_int_find(&map, 20);
        printf("\nFound: %d, (%g, %g), %d, %d, [%d: %d]\n", *i1.ref, i2.ref->x, i2.ref->y,
                                                            *i3.ref, *i4.ref,
                                                            i5.ref->first, i5.ref->second);
        // erase the elements found
        cset_int_erase_at(&set, i1);
        cvec_pnt_erase_at(&vec, i2);
        cdeq_int_erase_at(&deq, i3);
        clist_int_erase_at(&lst, i4);
        csmap_int_erase_at(&map, i5);

        printf("After erasing elements found:");
        printf("\n set:"); c_foreach (i, cset_int, set) printf(" %d", *i.ref);
        printf("\n vec:"); c_foreach (i, cvec_pnt, vec) printf(" (%g, %g)", i.ref->x, i.ref->y);
        printf("\n deq:"); c_foreach (i, cdeq_int, deq) printf(" %d", *i.ref);
        printf("\n lst:"); c_foreach (i, clist_int, lst) printf(" %d", *i.ref);
        printf("\n stk:"); c_foreach (i, cstack_int, stk) printf(" %d", *i.ref);
        printf("\n map:"); c_foreach (i, csmap_int, map) printf(" [%d: %d]", i.ref->first,
                                                                             i.ref->second);
    }
}

Output

Found: 20, (20, 2), 20, 20, [20: 2]
After erasing elements found:
 set: 10 30 40
 vec: (10, 1) (30, 3) (40, 4)
 deq: 5 10 30
 lst: 5 10 30
 stk: 10 20 30 40
 map: [10: 1] [30: 3] [40: 4]

Installation

Because it is headers-only, headers can simply be included in your program. The methods are static by default (some inlined). You may add the include folder to the CPATH environment variable to let GCC, Clang, and TinyC locate the headers.

If containers are used across several translation units with common instantiated container types, it is recommended to build as a "library" to minimize the executable size. To enable this mode, specify -DSTC_HEADER as a compiler option in your build environment and place all the instantiations of containers used in a single C-source file, e.g.:

// stc_libs.c
#define STC_IMPLEMENTATION
#include <stc/cstr.h>
#include "Point.h"

#define i_tag ii
#define i_key int
#define i_val int
#include <stc/cmap.h>  // cmap_ii: int => int

#define i_tag ix
#define i_key int64_t
#include <stc/cset.h>  // cset_ix

#define i_val int
#include <stc/cvec.h>  // cvec_int

#define i_tag pnt
#define i_val Point
#include <stc/clist.h> // clist_pnt

The emplace versus non-emplace container methods

STC, like c++ STL, has two sets of methods for adding elements to containers. One set begins with emplace, e.g. cvec_X_emplace_back(). This is a convenient alternative to cvec_X_push_back() when dealing non-trivial container elements, e.g. strings, shared pointers or other elements using dynamic memory or shared resources.

The emplace methods constructs or clones the given elements before they are added to the container. In contrast, the non-emplace methods moves the given elements into the container. For containers of integral or trivial element types, emplace and corresponding non-emplace methods are identical.

non-emplace: Move	emplace: Clone	Container
insert()	emplace()	cmap, csmap, cset, csset, cdeq, clist, cvec
insert_or_assign(), put()	emplace_or_assign()	cmap, csmap
push()	emplace()	cqueue, cpque, cstack
push_back()	emplace_back()	cdeq, clist, cvec
push_front()	emplace_front()	cdeq, clist

Strings are the most commonly used non-trivial data type. STC containers have proper pre-defined definitions for cstr container elements, so they are fail-safe to use both with the emplace and non-emplace methods:

#define i_val_str       // special macro to enable container of cstr
#include <stc/cvec.h>   // vector of string (cstr)
...
c_autovar (cvec_str vec = cvec_str_init(), cvec_str_del(&vec))   // defer vector destructor to end of block
c_autovar (cstr s = cstr_lit("a string literal"), cstr_del(&s))  // cstr_lit() for literals; no strlen() usage
{
    const char* hello = "Hello";
    cvec_str_push_back(&vec, cstr_from(hello);    // construct and add string from const char*
    cvec_str_push_back(&vec, cstr_clone(s));      // clone and add an existing cstr

    cvec_str_emplace_back(&vec, "Yay, literal");  // internally constructs cstr from string-literal
    cvec_str_emplace_back(&vec, cstr_clone(s));   // <-- COMPILE ERROR: expects const char*
    cvec_str_emplace_back(&vec, s.str);           // Ok: const char* input type.
}

This is made possible because the type configuration may be given an optional conversion/"rawvalue"-type as template parameter, along with a back and forth conversion methods to the container value type.

Hence, i_val x = ..., y = i_valfrom(i_valto(&x)) works as a clone function, where the output of i_valto() is type i_valraw. Function i_valfrom() is a clone function when i_valraw/i_valto is undefined (i_valraw defaults to i_val). Same for i_key.

Rawvalues are also beneficial for lookup and map insertions. The emplace methods constructs cstr-objects from the rawvalues, but only when required:

cmap_str_emplace(&map, "Hello", "world");
// Two cstr-objects were constructed by emplace

cmap_str_emplace(&map, "Hello", "again");
// No cstr was constructed because "Hello" was already in the map.

cmap_str_emplace_or_assign(&map, "Hello", "there");
// Only cstr_from("there") constructed. "world" was destructed and replaced.

cmap_str_insert(&map, cstr_from("Hello"), cstr_from("you"));
// Two cstr's constructed outside call, but both destructed by insert
// because "Hello" existed. No mem-leak but less efficient.

it = cmap_str_find(&map, "Hello");
// No cstr constructed for lookup, although keys are cstr-type.

Apart from strings, maps and sets are normally used with trivial value types. However, the last example on the cmap page demonstrates how to specify a map with non-trivial keys.

Erase methods

Name	Description	Container
erase()	key based	csmap, csset, cmap, cset, cstr
erase_at()	iterator based	csmap, csset, cmap, cset, cvec, cdeq, clist
erase_range()	iterator based	csmap, csset, cvec, cdeq, clist
erase_n()	index based	cvec, cdeq, cstr
remove()	remove all matching values	clist

Forward declaring containers

It is possible to forward declare containers. This is useful when a container is part of a struct, but still not expose or include the full implementation / API of the container.

// Header file
#include <stc/forward.h> // only include data structures
forward_cstack(cstack_pnt, struct Point); // declare cstack_pnt and cstack_pnt_value_t, cstack_pnt_iter_t;
                                          // the element may be forward declared type as well
typedef struct Dataset {
    cstack_pnt vertices;
    cstack_pnt colors;
} Dataset;

...
// Implementation
#define i_fwd               // flag that the container was forward declared.
#define i_val struct Point
#define i_tag pnt
#include <stc/cstack.h>

User-defined container type name

Define i_cnt instead of i_tag:

#define i_cnt myvec
#define i_val int
#include <stc/cvec.h>

myvec vec = myvec_init();
myvec_push_back(&vec, 1);

Memory efficiency

cstr, cvec: Type size: 1 pointer. The size and capacity is stored as part of the heap allocation that also holds the vector elements.
clist: Type size: 1 pointer. Each node allocates a struct which stores the value and next pointer.
cdeq: Type size: 2 pointers. Otherwise like cvec.
cmap: Type size: 4 pointers. cmap uses one table of keys+value, and one table of precomputed hash-value/used bucket, which occupies only one byte per bucket. The closed hashing has a default max load factor of 85%, and hash table scales by 1.6x when reaching that.
csmap: Type size: 1 pointer. csmap manages its own array of tree-nodes for allocation efficiency. Each node uses only two 32-bit ints for child nodes, and one byte for level.
carr2, carr3: Type size: 1 pointer plus dimension variables. Arrays are allocated as one contiguous block of heap memory, and one allocation for pointers of indices to the array.
csptr: Type size: 2 pointers, one for the data and one for the reference counter.

Kamilcuk/STC