用C++写一个vector

在C语言中，没有直接支持向量的数据类型，但可以通过结构体和动态内存分配来实现类似的功能。以下是一个简单的向量结构体和相应的函数实现：

#include <stdio.h>
#include <stdlib.h>

typedef struct {
    int* data;
    int size;
    int capacity;
} Vector;

void vector_init(Vector* vec) {
    vec->data = NULL;
    vec->size = 0;
    vec->capacity = 0;
}

void vector_append(Vector* vec, int value) {
    if (vec->size == vec->capacity) {
        int new_capacity = vec->capacity == 0 ? 1 : vec->capacity * 2;
        int* new_data = (int*)realloc(vec->data, new_capacity * sizeof(int));
        if (new_data == NULL) {
            printf("Error: Failed to allocate memory for vector.\n");
            exit(1);
        }
        vec->data = new_data;
        vec->capacity = new_capacity;
    }
    vec->data[vec->size++] = value;
}

int vector_get(Vector* vec, int index) {
    if (index < 0 || index >= vec->size) {
        printf("Error: Index out of bounds.\n");
        exit(1);
    }
    return vec->data[index];
}

void vector_set(Vector* vec, int index, int value) {
    if (index < 0 || index >= vec->size) {
        printf("Error: Index out of bounds.\n");
        exit(1);
    }
    vec->data[index] = value;
}

void vector_free(Vector* vec) {
    free(vec->data);
    vec->data = NULL;
    vec->size = 0;
    vec->capacity = 0;
}

使用示例：

int main() {
    Vector vec;
    vector_init(&vec);
    vector_append(&vec, 1);
    vector_append(&vec, 2);
    vector_append(&vec, 3);
    printf("Vector size: %d\n", vec.size);
    printf("Vector capacity: %d\n", vec.capacity);
    printf("Vector elements:");
    for (int i = 0; i < vec.size; i++) {
        printf(" %d", vector_get(&vec, i));
    }
    printf("\n");
    vector_set(&vec, 1, 4);
    printf("Vector elements:");
    for (int i = 0; i < vec.size; i++) {
        printf(" %d", vector_get(&vec, i));
    }
    printf("\n");
    vector_free(&vec);
    return 0;
}

输出结果：

Vector size: 3
Vector capacity: 4
Vector elements: 1 2 3
Vector elements: 1 4 3