generic vector template in ANSI C

vector.h

/*

https://gist.github.com/pervognsen/c56d4ddce94fbef3c80e228b39efc028
https://gist.github.com/pervognsen/6f295f356010186f3c350f31fbeec28b

*/

/* 
EXAMPLE

#define VEC_NAME vec_int
#define VEC_TYPE int
#define VEC_IMPLEMENTATION 1

#include "vector.h"
...

vec_int v;
vec_int_init(&v);


int i;
for (i = 0; i < 128; ++i)
{
    vec_int_push(&v, i);
    printf("%i ", v.capacity);
}

*/

#ifndef VEC_NAME
#error "must define vector name"
#endif

#ifndef VEC_TYPE
#error "must define vector type"
#endif

#include <stdlib.h>
#include <assert.h>

/* Two levels of macros to expand NAME variables.
   See: https://gcc.gnu.org/onlinedocs/cpp/Stringizing.html#Stringizing */

#define INNER_NS(NAME, FUNC) NAME ## _ ## FUNC
#define NS(NAME, FUNC) INNER_NS(NAME, FUNC)

typedef struct
{
    VEC_TYPE* data;
    size_t size;
    size_t capacity;
} VEC_NAME;


void NS(VEC_NAME, init)(VEC_NAME* v);
void NS(VEC_NAME, init_opt)(VEC_NAME* v, size_t capacity);
void NS(VEC_NAME, shutdown)(VEC_NAME* v);
void NS(VEC_NAME, push)(VEC_NAME* v, VEC_TYPE e);
VEC_TYPE NS(VEC_NAME, pop)(VEC_NAME* v);
void NS(VEC_NAME, reserve)(VEC_NAME* v, size_t capacity);


#ifdef VEC_IMPLEMENTATION

void NS(VEC_NAME, init)(VEC_NAME* v)
{
    NS(VEC_NAME, init_opt)(v, 16);
}


void NS(VEC_NAME, init_opt)(VEC_NAME* v, size_t capacity)
{
    v->capacity = capacity;
    v->size = 0;
    v->data = malloc(sizeof(VEC_TYPE) * capacity);
}


void NS(VEC_NAME, shutdown)(VEC_NAME* v)
{
    free(v->data);
}

void NS(VEC_NAME, push)(VEC_NAME* v, VEC_TYPE e)
{
    if (v->size + 1 > v->capacity)
    {
        v->capacity = (v->capacity * 3) / 2;
        v->data = realloc(v->data, sizeof(VEC_TYPE) * v->capacity);
    }

    v->data[v->size++] = e;
}

VEC_TYPE NS(VEC_NAME, pop)(VEC_NAME* v)
{
    assert(v->size > 0);

    VEC_TYPE r = v->data[--v->size];

    if (v->size > 16 && v->size <= v->capacity / 4)
    {
        v->capacity = v->capacity / 2;
        v->data = realloc(v->data, sizeof(VEC_TYPE) * v->capacity);
    }

    return r;
}

void NS(VEC_NAME, reserve)(VEC_NAME* v, size_t capacity)
{
    if (capacity <= v->capacity) return;
    v->capacity = capacity;
    v->data = realloc(v->data, sizeof(VEC_TYPE) * v->capacity);
}


#endif


#undef VEC_NAME
#undef VEC_TYPE
#undef NS
#undef INNER_NS