C/C++ operator关键字

最新推荐文章于 2024-07-11 15:48:51 发布

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最新推荐文章于 2024-07-11 15:48:51 发布

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分类专栏： C/C++

本文链接：https://blog.youkuaiyun.com/zz_hh_uu_/article/details/99435314

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本文详细介绍了如何使用C++实现矩阵乘法，包括矩阵类的定义、乘法函数的实现以及随机填充矩阵的方法。此外，还展示了如何创建可变长度的动态数组，包括构造函数、复制构造函数、赋值运算符重载和push_back方法。

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C++ 矩阵相乘

#include <iostream>
using namespace std;
class Matrix{
    float *data;
public:
    size_t n,m;
    Matrix(size_t r,size_t c):data(new float[r*c]),n(r),m(c){}
    ~Matrix() {delete[] data;}
    float& operator() (size_t x,size_t y){
        return data[x*m+y];
    }
    float operator() (size_t x,size_t y) const{
        return data[x*m+y];
    }
};

float dot(const Matrix &a,const Matrix& b) {
    Matrix c(a.n,b.m);
    for (size_t i=0;i<a.n;++i)
        for (size_t j=0;j<b.m;++j){
            float s = 0;
            for (size_t k=0;k<a.m;++k)
                s += a(i,k) * b(k,j);
            c(i,j) = s;
        }
    return c(0,0);
}

void fill_rand(Matrix &a){
    for (size_t i=0;i<a.n;++i){
        for (size_t j = 0;j<a.m;++j)
            a(i,j) = rand() / static_cast<float>(RAND_MAX) * 2 - 1;
    }
}

int main(){
    srand((unsigned)time(NULL));
    const int n = 100,p = 200 , m = 50, T = 100;
    Matrix a(n,p),b(p,m);
    fill_rand(a);
    fill_rand(b);
    auto st = chrono::system_clock::now();
    float s = 0;
    for (int i = 0; i < T; ++i) {
        s += dot(a, b);
    }
    auto ed = chrono::system_clock::now();
    chrono::duration<double> diff = ed-st;
    cerr << s << endl;
    cout << T << " loops. average " << diff.count() * 1e6 / T << "us" << endl;
}

335.764
100 loops. average 10071.3us

C++实现可变长度的动态数组

#include <iostream>
#include <cstring>
using namespace std;

class CArray
{
    int size;
    int *ptr;

public:
    CArray(int s = 0);
    CArray(CArray & a);
    ~CArray();
    void push_back(int v);
    CArray& operator = (const CArray &a);
    int length() const{return size;}
    int &operator[](int i)
    {
        return ptr[i];
    };
};

CArray::CArray(int s) : size(s)
{
   if(s == 0)
       ptr = NULL;
   else
       ptr = new int[s];
}

CArray::CArray(CArray & a)
{
    if(!a.ptr){
        ptr = NULL;
        size = 0;
        return;
    }
    ptr = new int[a.size];
    memcpy(ptr,a.ptr, sizeof(int) * a.size);
    size = a.size;
}

CArray::~CArray() {
    if(ptr) delete[] ptr;
}

CArray& CArray::operator=(const CArray &a) {
    if(ptr == a.ptr)
        return *this;
    if (a.ptr == NULL){
        if (ptr)
            delete[] ptr;
        ptr = NULL;
        size = 0;
        return *this;
    }
    if (size < a.size){
        if(ptr)
            delete[] ptr;
        ptr = new int[a.size];
    }
    memcpy(ptr,a.ptr, sizeof(int)*a.size);
    size = a.size;
    return *this;
}

void CArray::push_back(int v) {
    if(ptr){
        int* tmpPtr = new int[size + 1];
        memcpy(tmpPtr,ptr, sizeof(int) * size);
        delete[] ptr;
        ptr = tmpPtr;
    }
    else
        ptr = new int[1];
    ptr[size++] = v;
}

int main(){
    CArray a;
    for(int i=0; i<5 ; ++i)
        a.push_back(i);
    CArray a2,a3;
    a2 = a;

    for(int i = 0;i < a.length(); ++i)
        cout << a2[i] << " ";
    a2 = a3;

    for(int i=0;i<a2.length();++i)
        cout << a2[i] << " ";
    cout << endl;
    a[3] = 100;

    CArray a4(a);
    for(int i = 0;i<a4.length(); ++i)
        cout << a4[i] << " ";

    return 0;
}