Question

语言：C ++ 系统：Linux：编译：g ++ prog.cpp -o prog

这是问题所在。我有一个程序，让用户插入两个矩阵的大小（我保持矩阵1D而不是2D作为练习）。代码中给我问题的部分通常很好，除非我输入：

当我这样做时，输出是printf（“4”）和printf（“5”）之间的分段错误。

#include <iostream>

int main(void)
{
int oneColoumn, oneRow, twoColoumn, twoRow;

std::cout << "\nHow many coloumns do you want for the first matrix?" << std::endl;
std::cin >> oneColoumn;

std::cout << "\nHow many rows do you want for the first matrix?" << std::endl;
std::cin >> oneRow;

std::cout << "\nHow many coloumns do you want for the second matrix?" << std::endl;
std::cin >> twoColoumn;

std::cout << "\nHow many rows do you want for the second matrix?" << std::endl;
std::cin >> twoRow;

int firstMatrix[oneColoumn*oneRow];
int secondMatrix[twoColoumn*twoRow];

for(int i=0; i < oneColoumn; i++)
{
    for(int j=0; j < oneRow; j++)
    {
        std::cout << "Insert a number for the first matrix";
        std::cin >> firstMatrix[i*oneColoumn + j];
    }   
}
printf("1");
for(int i=0; i < twoColoumn; i++)
{printf("2");
    for(int j=0; j < twoRow; j++)
    {printf("3");
        std::cout << "Insert a number for the second matrix";
        printf("4");
        std::cin >> secondMatrix[i*twoColoumn + j];
        printf("5");
    }   
}

int threeColoumn, threeRow;
if(oneColoumn>twoColoumn)
    threeColoumn=twoColoumn;
if(oneRow>twoRow)
    threeRow=twoRow;
int thirdMatrix[threeColoumn*threeRow];

char choice;
std::cout<<"Do you want to add or multiply the two matrices?(a/m)"<<std::endl;
std::cin>>choice;
if(choice=='a')
{
    std::cout<<"The two matrices have been added"<<std::endl;
    //Addition(firstMatrix,oneRow,oneColoumn,secondMatrix,twoRow,twoColoumn,thirdMatrix,threeRow,threeColoumn);
}
else if(choice=='m')
{
    std::cout<<"The two matrices have been multiplied"<<std::endl;
    //Multiplication(firstMatrix,oneRow,oneColoumn,secondMatrix,twoRow,twoColoumn,thirdMatrix,threeRow,threeColoumn);
    }

}

Answer 1

您有阵列索引问题：

for(int i=0; i < oneColoumn; i++)
{
    for(int j=0; j < oneRow; j++)
    {
        std::cout << "Insert a number for the first matrix";
        std::cin >> firstMatrix[i*oneColoumn + j];
    }   
}

内循环完成一次后，迭代一次。

在内循环的两次完成之后，你已经迭代了2 * oneRow次。

... 等

你想：

    firstMatrix[i*oneRow + j]

此外，正如其他人所指出的，以下两行将堆栈上的数组声明为VLA（可变长度数组），因为值oneColumn和oneRow由用户提供，而不是直到运行时才知道。

int firstMatrix[oneColoumn*oneRow];
int secondMatrix[twoColoumn*twoRow];

不一定支持，但可能取决于您的编译器。对于gcc，请参阅https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html。还可以看到：What's the difference between a VLA and dynamic memory allocation via malloc?

为什么“std :: cin＆gt;＆gt; secondMatrix [i * twoColoumn + j];”给我分段错误

1 个答案: