Calcifa97
Calcifa97
采纳率100%
2019-12-13 16:11 阅读 231

请问为什么用new建立动态二维数组就会报错,用malloc就不会报错。

请问为什么用注释掉的部分建立动态二维数组就会报错,用malloc就不会报错?

void Matrix()
{
    int i;
    //double** P_ca_x = new double* [Times];
    //double** P_ca_y = new double* [Times];
    //double** P_ca_z = new double* [Times];
    //double** v_ca_x = new double* [Times];
    //double** v_ca_y = new double* [Times];
    //double** v_ca_z = new double* [Times];
    //double** v_ca = new double* [Times];
    P_ca_x = (double**)malloc(sizeof(double*) * Times);
    P_ca_y = (double**)malloc(sizeof(double*) * Times);
    P_ca_z = (double**)malloc(sizeof(double*) * Times);
    v_ca_x = (double**)malloc(sizeof(double*) * Times);
    v_ca_y = (double**)malloc(sizeof(double*) * Times);
    v_ca_z = (double**)malloc(sizeof(double*) * Times);
    v_ca = (double**)malloc(sizeof(double*) * Times);
    for (i = 0; i < Times; i++)
    {
        //P_ca_x[i] = new double[Num];
        //P_ca_y[i] = new double[Num];
        //P_ca_z[i] = new double[Num];
        //v_ca_x[i] = new double[Num];
        //v_ca_y[i] = new double[Num];
        //v_ca_z[i] = new double[Num];
        //v_ca[i] = new double[Num];
        P_ca_x[i] = (double*)malloc(sizeof(double) * Num);
        P_ca_y[i] = (double*)malloc(sizeof(double) * Num);
        P_ca_z[i] = (double*)malloc(sizeof(double) * Num);
        v_ca_x[i] = (double*)malloc(sizeof(double) * Num);
        v_ca_y[i] = (double*)malloc(sizeof(double) * Num);
        v_ca_z[i] = (double*)malloc(sizeof(double) * Num);
        v_ca[i] = (double*)malloc(sizeof(double) * Num);
    }
}
void Delete()
{
    int i;
    for (i = 0; i < Times; i++)
    {
        //delete[] P_ca_x[i];
        //delete[] P_ca_y[i];
        //delete[] P_ca_z[i];
        //delete[] v_ca_x[i];
        //delete[] v_ca_y[i];
        //delete[] v_ca_z[i];
        //delete[] v_ca[i];
        free(P_ca_x[i]);
        free(P_ca_y[i]);
        free(P_ca_z[i]);
        free(v_ca_x[i]);
        free(v_ca_y[i]);
        free(v_ca_z[i]);
        free(v_ca[i]);
    }
    //delete[] P_ca_x;
    //delete[] P_ca_y;
    //delete[] P_ca_z;
    //delete[] v_ca_x;
    //delete[] v_ca_y;
    //delete[] v_ca_z;
    //delete[] v_ca;
    free(P_ca_x);
    free(P_ca_y);
    free(P_ca_z);
    free(v_ca_x);
    free(v_ca_y);
    free(v_ca_z);
    free(v_ca);
}

在对数组赋值时报错,用malloc则不会报错
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2条回答 默认 最新

  • 已采纳
    J4cks0n J4cks0n 2019-12-13 16:40

    不会报错把,麻烦把错误信息贴一下。不应该报错的

    你先把下面的程序编译一下,如果没报错就不是new的问题

    #include <iostream>
    #include <string.h>
    
    using namespace std;
    
    int main()
    {
        //申请
        double ** a = new double*[5];
        for(int i = 0; i<5; ++i)
        {
            a[i] = new double[6];
            memset(a[i], 0, sizeof(double)*6);
        }
    
        //赋值
        for(int i = 0; i<5; ++i)
            for(int j = 0; j < 6; ++j)
                a[i][j] = i*j*1.3;
    
        //输出
        for(int i = 0; i<5; ++i)
        {
            for(int j = 0; j < 6; ++j)
                cout<<a[i][j]<<" ";
            cout<<endl;
        }
    
        //删除
        for(int i = 0; i<5; ++i)
        {
            delete[] a[i]; 
        }
        delete[] a;
    }
    
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  • rubikchen 502203305 2019-12-13 16:42

    类型不一致。new的数组是有长度的,而malloc指针是没有长度的。new后用对应类型保存,或者强转。

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