STC - Smart Template Containers for C

News: Version 3 released (Jan 2022)

This version introduces lots of enhancements, bugfixes and additions. There are also a number of breaking changes and a migration guide from version 2 to 3. With version 3, the API is freezed as far as possible. Any changes will be handled with long lasting deprecations, so you may develop production code using it.

Introduction

STC is 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. It takes some inspirations from Rust and Python too.

It is a compact, header-only library which includes the all the major "standard" data containers except for the multimap/set variants. However, there are examples on how to create multimaps in the examples folder.

For an introduction to templated containers, please read the blog by Ian Fisher on type-safe generic data structures in C. Note that STC does not use long macro expansions anymore, but relies on one or more inclusions of the same file, which by the compiler is seen as different code because of macro name substitutions.

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_{arg} 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 carc.
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_type FVec    // if not defined, vector type would be cvec_float
#define i_val float    // element type
#include <stc/cvec.h>  // defines the FVec type

int main(void) {
    FVec vec = FVec_init();
    FVec_push_back(&vec, 10.f);
    FVec_push_back(&vec, 20.f);
    FVec_push_back(&vec, 30.f);

    for (size_t i = 0; i < FVec_size(vec); ++i)
        printf(" %g", vec.data[i]);
    FVec_drop(&vec); // free memory
}

A "better" way to write the same code is:

int main(void) {
    c_auto (FVec, vec) // RAII - create and destroy vec
    {
        c_apply(v, FVec_push_back(&vec, v), float, {10.f, 20.f, 30.f});

        c_foreach (i, FVec, vec) // generic iteration and element access
            printf(" %g", *i.ref);
    }
}

In order to include two cvecs with different element types, include cvec.h twice. For struct, a i_cmp compare function is required to enable sorting and searching (< and == operators is default and works for integral types only). Alternatively, #define i_opt c_no_cmp to disable methods using comparison.

Similarly, if a destructor i_valdrop is defined, either define a i_valfrom construct/clone function or #define i_opt c_no_clone to disable cloning and emplace methods. Unless these requirements are met, compile errors are generated.

#define i_val struct One
#define i_opt c_no_cmp
#define i_tag one
#include <stc/cvec.h>

#define i_val struct Two
#define i_opt c_no_cmp
#define i_tag two
#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_cmp(const struct Point* a, const struct Point* b) {
    int cmp = c_default_cmp(&a->x, &b->x);
    return cmp ? cmp : c_default_cmp(&a->y, &b->y);
}

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

#define i_val struct Point
#define i_cmp Point_cmp
#define i_tag pnt
#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 drop (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(v, cset_int_insert(&set, v), int, {10, 20, 30});
        c_apply(v, cvec_pnt_push_back(&vec, v), struct Point, { {10, 1}, {20, 2}, {30, 3} });
        c_apply(v, cdeq_int_push_back(&deq, v), int, {10, 20, 30});
        c_apply(v, clist_int_push_back(&lst, v), int, {10, 20, 30});
        c_apply(v, cstack_int_push(&stk, v), int, {10, 20, 30});
        c_apply(v, csmap_int_insert(&map, c_pair(v)), 
            csmap_int_raw, { {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 i1 = cset_int_find(&set, 20);
        cvec_pnt_iter i2 = cvec_pnt_find(&vec, (struct Point){20, 2});
        cdeq_int_iter i3 = cdeq_int_find(&deq, 20);
        clist_int_iter i4 = clist_int_find(&lst, 20);
        csmap_int_iter 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_key int
#define i_val int
#define i_tag ii
#include <stc/cmap.h>  // cmap_ii: int => int

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

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

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

Specifying template parameters

Each templated type requires one #include, even if it's the same container base type, as described earlier. The template parameters are given by a #define i_xxxx statement, where xxxx is the parameter name. The list of template parameters:

i_key - Element key type for map/set only. [required].
i_val - Element value type. [required]. For cmap/csmap, it is the mapped value type.
i_cmp - Three-way comparison of two i_keyraw or i_valraw pointers - [required] for non-integral valraw types unless i_opt c_no_cmp is defined.
i_hash - Hash function taking i_keyraw * and a size - defaults to !i_cmp. [required] for non-POD valraw type.
i_eq - Equality comparison of two i_keyraw * - defaults to !i_cmp. Companion with i_hash.

Properties:

i_tag - Container type name tag. Defaults to same as i_key
i_type - Full container type name. Alternative to i_tag.
i_opt - Boolean properties: may combine c_no_cmp, c_no_clone, c_no_atomic, c_is_fwd, c_static, c_header, c_implement with | separator.

Key:

i_keydrop - Destroy map/set key func - defaults to empty destructor.
i_keyraw - Convertion "raw" type - defaults to i_key type.
i_keyfrom - Convertion func i_key <= i_keyraw. [required] if i_keydrop is defined. Works as clone when i_keyraw not specified.
i_keyto - Convertion func i_key * => i_keyraw.

Val:

i_valdrop - Destroy mapped or value func - defaults to empty destruct.
i_valraw - Convertion "raw" type - defaults to i_val type.
i_valfrom - Convertion func i_val <= i_valraw. [required] if i_valdrop is defined. Works as clone when i_valraw not specified.
i_valto - Convertion func i_val * => i_valraw.

Special:

i_key_str - Define key type cstr and container i_tag = str. It binds type convertion from/to const char*, and the cmp, eq, hash, and keydrop functions.
i_key_arcbox TYPE - Define container key type where TYPE is a smart pointer carc or cbox. NB: not to be used when defining carc/cbox types themselves.
i_key_bind TYPE - General version of the two above - will auto-bind to standard named functions: TYPE_clone, TYPE_drop, TYPE_cmp, TYPE_eq, TYPE_hash. Only functions required by the particular container need to be defined (TYPE_drop is always used). E.g., only cmap and cset uses TYPE_hash and TYPE_eq. And cstack does not use TYPE_cmp. TYPE_clone is not used if #define i_opt c_no_clone is specified. Likewise, TYPE_cmp is not used if #define i_opt c_no_cmp is specified.
i_keyraw RAWTYPE - If defined along with i_key_bind, the two functions TYPE TYPE_from(i_valraw) and RAWTYPE TYPE_toraw(TYPE*) are expected instead of TYPE TYPE_clone(TYPE). Cloning is done by TYPE_from(TYPE_toraw(&val)). Functions cmp, eq and hash to be bound must have name/signature: int RAWTYPE_cmp(const RAWTYPE*, const RAWTYPE*), and similar for RAWTYPE_eq and RAWTYPE_hash.
i_val_str, i_val_bind, i_val_arcbox - Similar rules as for key.

Notes:

Instead of defining i_cmp, you may define i_opt c_no_cmp to disable searching and sorting functions.
Instead of defining i_*from, you may define i_opt c_no_clone to disable emplace and clone-functions.
If a destructor i_*drop is defined, then either i_*from or i_opt c_no_clone must be defined.

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 when they are added to the container. In contrast, the non-emplace methods moves the given elements into the container.

Note: For containers with integral/trivial element types, or when neither i_keyraw/i_valraw nor i_valfrom/i_valfrom are defined, the emplace functions are not available (or needed), as it can easier lead to mistakes.

non-emplace: Move	emplace: Embedded copy	Container
insert()	emplace()	cmap, csmap, cset, csset
insert_or_assign(), put()	emplace_or_assign(), put_raw()	cmap, csmap
push()	emplace()	cqueue, cpque, cstack
push_back(), push()	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_auto (cvec_str, vec)  // declare and call cvec_str_init() and defer cvec_str_drop(&vec)
c_autovar (cstr s = cstr_new("a string literal"), cstr_drop(&s))  // c_autovar is a more general c_auto.
{
    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 append a cstr

    cvec_str_emplace_back(&vec, "Yay, literal");  // internally constructs cstr from const char*
    cvec_str_emplace_back(&vec, cstr_clone(s));   // <-- COMPILE ERROR: expects const char*
    cvec_str_emplace_back(&vec, cstr_str(&s));    // 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_new("there") constructed. "world" was destructed and replaced.

cmap_str_insert(&map, cstr_new("Hello"), cstr_new("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, cstack_pnt_iter;
                                          // the element may be forward declared type as well
typedef struct Dataset {
    cstack_pnt vertices;
    cstack_pnt colors;
} Dataset;

...
// Implementation
#define c_opt c_is_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_type instead of i_tag:

#define i_type 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.
carc: Type size: 2 pointers, one for the data and one for the reference counter.

Version 3

Brief summary of changes

Renamed: all _del to _drop (like destructors in Rust).
Renamed: all _compare to _cmp
Renamed: i_equ to i_eq, and _equalto to _eq.
Renamed: i_cnt to i_type for defining the complete container type name.
Renamed: type csptr to carc (atomic reference counted) smart pointer.
Renamed: i_key_csptr / i_val_csptr to i_key_arcbox / i_val_arcbox for specifying carc and cbox values in containers.
Renamed: csptr_X_make() to carc_X_from().
Renamed: cstr_lit() to cstr_new(literal), and cstr_assign_fmt() to cstr_printf().
Renamed: c_default_fromraw() to c_default_from().
Changed: the c_apply macros API.
Replaced: csview_first_token() and csview_next_token() with one function: csview_token().
Added: checkauto tool for checking that c-source files uses c_auto* macros correctly.
Added: general i_key_bind / i_val_bind template parameters which auto-binds template functions.
Added: i_opt template parameter: compile-time options: c_no_cmp, c_no_clone, c_no_atomic, c_is_fwd; may be combined with |
Added: cbox type: smart pointer, similar to Rust Box and std::unique_ptr.
Added: c_forpair macro: for-loop with "structured binding"

Migration guide from version 2 to 3

Replace (regular expression) globally in code base (VS Code):

_del\b ⟶ _drop
_compare\b ⟶ _cmp
_rawvalue\b ⟶ _raw
_equ\b ⟶ _eq

Replace (whole word + match case):

i_keydel ⟶ i_keydrop
i_valdel ⟶ i_valdrop
i_cnt ⟶ i_type
cstr_lit ⟶ cstr_new
i_key_sptr ⟶ i_key_arcbox
i_val_sptr ⟶ i_val_arcbox

Non-regex, global match case replace:

csptr ⟶ carc

gerbenvoshol / STC