# STC [ccommon](../include/stc/ccommon.h): Generic algorithms and macros

The following macros are recommended to use, and they safe/have no side-effects.

## Scope macros (RAII)
### c_auto, c_with, c_scope, c_defer
General ***defer*** mechanics for resource acquisition. These macros allows you to specify the
freeing of the resources at the point where the acquisition takes place.
The **checkauto** utility described below, ensures that the `c_auto*` macros are used correctly.

| Usage                                  | Description                                               |
|:---------------------------------------|:----------------------------------------------------------|
| `c_with (Type var=init, drop)`         | Declare `var`. Defer `drop...` to end of scope            |
| `c_with (Type var=init, pred, drop)`   | Adds a predicate in order to exit early if init failed    |
| `c_auto (Type, var1,...,var4)`         | `c_with (Type var1=Type_init(), Type_drop(&var1))` ...    |
| `c_scope (init, drop)`                 | Execute `init` and defer `drop` to end of scope           |
| `c_defer (drop...)`                    | Defer `drop...` to end of scope                           |
| `continue`                             | Exit a block above without memory leaks                   |

For multiple variables, use either multiple **c_with** in sequence, or declare variable outside
scope and use **c_scope**. For convenience, **c_auto** support up to 4 variables.
```c
// `c_with` is similar to python `with`: it declares and can drop a variable after going out of scope.
bool ok = false;
c_with (uint8_t* buf = malloc(BUF_SIZE), buf != NULL, free(buf))
c_with (FILE* fp = fopen(fname, "rb"), fp != NULL, fclose(fp))
{
    int n = fread(buf, 1, BUF_SIZE, fp);
    if (n <= 0) continue; // auto cleanup! NB do not break or return here.
    ...
    ok = true;
}
return ok;

// `c_auto` automatically initialize and destruct up to 4 variables:
c_auto (cstr, s1, s2)
{
    cstr_append(&s1, "Hello");
    cstr_append(&s1, " world");

    cstr_append(&s2, "Cool");
    cstr_append(&s2, " stuff");

    printf("%s %s\n", cstr_str(&s1), cstr_str(&s2));
}

// `c_with` is a general variant of `c_auto`:
c_with (cstr str = cstr_lit("Hello"), cstr_drop(&str))
{
    cstr_append(&str, " world");
    printf("%s\n", cstr_str(&str));
}

// `c_scope` is like `c_with` but works with an already declared variable.
static pthread_mutex_t mut;
c_scope (pthread_mutex_lock(&mut), pthread_mutex_unlock(&mut))
{
    /* Do syncronized work. */
}

// `c_defer` executes the expressions when leaving scope. Prefer c_with or c_scope.
cstr s1 = cstr_lit("Hello"), s2 = cstr_lit("world");
c_defer (cstr_drop(&s1), cstr_drop(&s2))
{
    printf("%s %s\n", cstr_str(&s1), cstr_str(&s2));
}
```
**Example**: Load each line of a text file into a vector of strings:
```c
#include <errno.h>
#include <stc/cstr.h>

#define i_val_str
#include <stc/cvec.h>

// receiver should check errno variable
cvec_str readFile(const char* name)
{
    cvec_str vec = cvec_str_init(); // returned

    c_with (FILE* fp = fopen(name, "r"), fp != NULL, fclose(fp))
    c_with (cstr line = cstr_NULL, cstr_drop(&line))
        while (cstr_getline(&line, fp))
            cvec_str_emplace_back(&vec, cstr_str(&line));
    return vec;
}

int main()
{
    c_with (cvec_str x = readFile(__FILE__), cvec_str_drop(&x))
        c_foreach (i, cvec_str, x)
            printf("%s\n", cstr_str(i.ref));
}
```
## Loop abstraction macros

### c_foreach, c_forpair

| Usage                                    | Description                     |
|:-----------------------------------------|:--------------------------------|
| `c_foreach (it, ctype, container)`       | Iteratate all elements          |
| `c_foreach (it, ctype, it1, it2)`        | Iterate the range [it1, it2)    |
| `c_forpair (key, val, ctype, container)` | Iterate with structured binding |

```c
#define i_key int
#define i_val int
#define i_tag ii
#include <stc/csmap.h>
...
csmap_ii map = c_make(csmap_ii, { {23,1}, {3,2}, {7,3}, {5,4}, {12,5} });

c_foreach (i, csmap_ii, map)
    printf(" %d", i.ref->first);
// 3 5 7 12 23
// same without using c_foreach:
for (csmap_ii_iter i = csmap_ii_begin(&map); i.ref; csmap_ii_next(&i))
    printf(" %d", i.ref->first);

csmap_ii_iter it = csmap_ii_find(&map, 7);
// iterate from it to end
c_foreach (i, csmap_ii, it, csmap_ii_end(&map))
    printf(" %d", i.ref->first);
// 7 12 23

// structured binding:
c_forpair (id, count, csmap_ii, map)
    printf(" (%d %d)", *_.id, *_.count);
// (3 2) (5 4) (7 3) (12 5) (23 1)
```

### c_forrange
Abstraction for iterating sequence of integers. Like python's **for** *i* **in** *range()* loop.

| Usage                                        | Python equivalent                    |
|:---------------------------------------------|:-------------------------------------|
| `c_forrange (stop)`                          | `for _ in range(stop):`              |
| `c_forrange (i, stop) // i type = long long` | `for i in range(stop):`              |
| `c_forrange (i, start, stop)`                | `for i in range(start, stop):`       |
| `c_forrange (i, start, stop, step)`          | `for i in range(start, stop, step):` |

```c
c_forrange (5) printf("x");
// xxxxx
c_forrange (i, 5) printf(" %lld", i);
// 0 1 2 3 4
c_forrange (i, -3, 3) printf(" %lld", i);
// -3 -2 -1 0 1 2
c_forrange (i, 30, 0, -5) printf(" %lld", i);
// 30 25 20 15 10 5
```

### c_forlist
Iterate compound literal array elements. Additional to `i.ref`, you can access `i.data`, `i.size`, and `i.index` of the input list/element.
```c
// apply multiple push_backs
c_forlist (i, int, {1, 2, 3})
    cvec_i_push_back(&vec, *i.ref);

// insert in existing map
c_forlist (i, cmap_ii_raw, { {4, 5}, {6, 7} })
    cmap_ii_insert(&map, i.ref->first, i.ref->second);

// string literals pushed to a stack of cstr:
c_forlist (i, const char*, {"Hello", "crazy", "world"})
    cstack_str_emplace(&stk, *i.ref);

// reverse the list:
c_forlist (i, int, {1, 2, 3})
    cvec_i_push_back(&vec, i.data[i.size - 1 - i.index]);
```

### c_forfilter
Iterate containers with stop-criteria and chained range filtering.

| Usage                                               | Description                            |
|:----------------------------------------------------|:---------------------------------------|
| `c_forfilter (it, ctype, container, filter)`        | Filter out items in chain with &&      |
| `c_forwhile (it, ctype, start, pred)`               | Iterate until pred is false            |

| Built-in filter                   | Description                          |
|:----------------------------------|:-------------------------------------|
| `c_flt_skip(it, numItems)`        | Skip numItems (inc count)            |
| `c_flt_take(it, numItems)`        | Take numItems (inc count)            |
| `c_flt_skipwhile(it, predicate)`  | Skip items until predicate is false  |
| `c_flt_takewhile(it, predicate)`  | Take items until predicate is false  |
| `c_flt_count(it)`                 | Increment current and return value   |
| `c_flt_last(it)`                  | Get value of last count/skip/take    |
```c
// Example:
#include <stc/algo/crange.h>
#include <stc/algo/filter.h>
#include <stdio.h>

bool isPrime(long long i) {
    for (long long j=2; j*j <= i; ++j)
        if (i % j == 0) return false;
    return true;
}
int main() {
    // Get 10 prime numbers starting from 1000.
    // Skip the first 24 primes, then select every 15th prime.
    crange R = crange_make(1001, INT32_MAX, 2);

    c_forfilter (i, crange, R,
                    isPrime(*i.ref)
                 && c_flt_skip(i, 24)
                 && c_flt_count(i) % 15 == 1
                 && c_flt_take(i, 10))
        printf(" %lld", *i.ref);
    puts("");
}
// out: 1171 1283 1409 1493 1607 1721 1847 1973 2081 2203
```
Note that `c_flt_take()` and `c_flt_takewhile()`breaks the loop on false.

## Generators

### crange
A number sequence generator type, similar to [boost::irange](https://www.boost.org/doc/libs/release/libs/range/doc/html/range/reference/ranges/irange.html). The **crange_value** type is `long long`. Below *start*, *stop*, and *step* are of type *crange_value*:
```c
crange&     crange_obj(...)                 // create a compound literal crange object
crange      crange_make(stop);              // will generate 0, 1, ..., stop-1
crange      crange_make(start, stop);       // will generate start, start+1, ... stop-1
crange      crange_make(start, stop, step); // will generate start, start+step, ... upto-not-including stop
                                            // note that step may be negative.
crange_iter crange_begin(crange* self);
crange_iter crange_end(crange* self);
void        crange_next(crange_iter* it);

// 1. All primes less than 32:
crange r1 = crange_make(3, 32, 2);
printf("2"); // first prime
c_forfilter (i, crange, r1, isPrime(*i.ref))
    printf(" %lld", *i.ref);
// 2 3 5 7 11 13 17 19 23 29 31

// 2. The 11 first primes:
printf("2");
c_forfilter (i, crange, crange_obj(3, INT64_MAX, 2)
              , isPrime(*i.ref)
             && c_flt_take(10))
    printf(" %lld", *i.ref);
// 2 3 5 7 11 13 17 19 23 29 31
```
## Algorithms

### c_make, c_new, c_delete

- *c_make(C, {...})*: Make any container from an initializer list. Example:
```c
#define i_val_str  // cstr value type
#include <stc/cset.h>

#define i_key int
#define i_val int
#include <stc/cmap.h>
...
// Initializes with const char*, internally converted to cstr!
cset_str myset = c_make(cset_str, {"This", "is", "the", "story"});

int x = 7, y = 8;
cmap_int mymap = c_make(cmap_int, { {1, 2}, {3, 4}, {5, 6}, {x, y} });
```

- ***c_new(Type)***: Allocate *and init* a new object on the heap
- ***c_delete(Type, ptr)***: Drop *and free* an object allocated on the heap
```c
#include <stc/cstr.h>

cstr *stringptr = c_new(cstr, cstr_from("Hello"));
printf("%s\n", cstr_str(stringptr));
c_delete(cstr, stringptr);
```

### c_find_if, c_erase_if, c_eraseremove_if
Find or erase linearily in containers using a predicate
- For *c_find_if (iter, C, c, pred)*, ***iter*** must be declared outside/prior to call.
- Use *c_erase_if (iter, C, c, pred)* with **clist**, **cmap**, **cset**, **csmap**, and **csset**.
- Use *c_eraseremove_if (iter, C, c, pred)* with **cstack**, **cvec**, **cdeq**, and **cqueue**.
```c
// Search vec for first value > 2:
cvec_i_iter i;
c_find_if(i, cvec_i, vec, *i.ref > 2);
if (i.ref) printf("%d\n", *i.ref);

// Erase all values > 2 in vec:
c_eraseremove_if(i, cvec_i, vec, *i.ref > 2);

// Search map for a string containing "hello" and erase it:
cmap_str_iter it, it1 = ..., it2 = ...;
c_find_if(it, csmap_str, it1, it2, cstr_contains(it.ref, "hello"));
if (it.ref) cmap_str_erase_at(&map, it);

// Erase all strings containing "hello" in a sorted map:
c_erase_if(i, csmap_str, map, cstr_contains(i.ref, "hello"));
```

### c_swap, c_drop
```c
// Safe macro for swapping internals of two objects of same type:
c_swap(cmap_int, &map1, &map2);

// Drop multiple containers of same type:
c_drop(cvec_i, &vec1, &vec2, &vec3);
```

### General predefined template parameter functions
```c
int         c_default_cmp(const Type*, const Type*);
Type        c_default_clone(Type val);           // simple copy
Type        c_default_toraw(const Type* val);    // dereference val
void        c_default_drop(Type* val);           // does nothing

typedef     const char* crawstr;
int         crawstr_cmp(const crawstr* x, const crawstr* y);
bool        crawstr_eq(const crawstr* x, const crawstr* y);
uint64_t    crawstr_hash(const crawstr* x);
```

### c_malloc, c_calloc, c_realloc, c_free: customizable allocators
Memory allocator wrappers that uses signed sizes.

### c_arraylen
Return number of elements in an array. array must not be a pointer!
```c
int array[] = {1, 2, 3, 4};
intptr_t n = c_arraylen(array);
```

## The **checkauto** utility program (for RAII)
The **checkauto** program will check the source code for any misuses of the `c_auto*` macros which
may lead to resource leakages. The `c_auto*`- macros are implemented as one-time executed **for-loops**,
so any `return` or `break` appearing within such a block will lead to resource leaks, as it will disable
the cleanup/drop method to be called. A `break` may originally be intended to break a loop or switch
outside the `c_auto` scope.

NOTE: One must always make sure to unwind temporary allocated resources before a `return` in C. However, by using `c_auto*`-macros,
- it is much easier to automatically detect misplaced return/break between resource acquisition and destruction.
- it prevents forgetting to call the destructor at the end.

The **checkauto** utility will report any misusages. The following example shows how to correctly break/return
from a `c_auto` scope:
```c
int flag = 0;
for (int i = 0; i<n; ++i) {
    c_auto (cstr, text)
    c_auto (List, list)
    {
        for (int j = 0; j<m; ++j) {
            List_push_back(&list, i*j);
            if (cond1())
                break;  // OK: breaks current for-loop only
        }
        // WRONG:
        if (cond2())
            break;      // checkauto ERROR! break inside c_auto.

        if (cond3())
            return -1;  // checkauto ERROR! return inside c_auto

        // CORRECT:
        if (cond2()) {
            flag = 1;   // flag to break outer for-loop
            continue;   // cleanup and leave c_auto block
        }
        if (cond3()) {
            flag = -1;  // return -1
            continue;   // cleanup and leave c_auto block
        }
        ...
    }
    // do the return/break outside of c_auto
    if (flag < 0) return flag;
    else if (flag > 0) break;
    ...
}
```