C语言中填充vector/matrix后打印显示垃圾值问题求助

问题描述 #

尝试在函数间打印vector，但填充vector或matrix后，离开对应函数时数据会丢失，导致打印出随机垃圾值。以下是相关代码：

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

void menu();
void fillVector1(int vector[], int size);
void fillVector2(int vector[], int size);
void fillVector3(int vector[], int vector1[], int vector2[], int size);
void fillMatrix(int matrix[][5], int size);
void printVector(int vector[], int size);
void printMatrix(int matrix[][5], int size);

int main()
{
    menu();
    return 0;
}

void menu()
{
    int option;
    int vector1[10];
    int vector2[10];
    int vector3[20];
    int matrix[5][5];

    printf("ARRAYS MENU");
    printf("\n\t1.- Fill Vector 1\n\t2.- Fill Vector 2\n\t3.- Fill Vector 3\n\t4.- Print Vectors\n\t5.- Fill Matrix 4x4\n\t6.- Print Matrix\n\t0.- Close Program\n");
    printf("Select an option: ");
    scanf("%i", &option);

    switch (option)
    {
    case 1:
        fillVector1(vector1, 10);
        break;
    case 2:
        fillVector2(vector2, 10);
        break;
    case 3:
        fillVector3(vector3, vector1, vector2, 10);
        printVector(vector3, 10);
        break;
    case 4:
        printf("\n");
        printVector(vector1, 10);
        printf("\n");
        printVector(vector2, 10);
        printf("\n");
        printVector(vector3, 20);
        break;
    case 5:
        fillMatrix(matrix, 4);
        break;
    case 6:
        printMatrix(matrix, 4);
        break;
    case 0:
        printf("Thanks for using this program. Come back soon!");
        break;
    default:
        printf("Invalid option. Select another one.");
        break;
    }
}

void fillVector1(int vector[], int size)
{
    printf("Fill it only with numbers between 30 to 70\n");

    for (int i = 0; i < size; i++)
    {
        printf("Vector[%i]: ", i);
        scanf("%i", &vector[i]);

        if (vector[i] < 30 || vector[i] > 70)
        {
            printf("Value out of range. Please enter another number.\n");
            i--; // repeat last (incorrect) index
        }
    }
    menu();
}

void fillVector2(int vector[], int size)
{
    printf("Vector filled with random numbers between 1 to 20");

    int checkRepeated;

    srand(time(NULL));
    for (int i = 0; i < size; i++)
    {
        // function to avoid repeated number
        do
        {
            checkRepeated = 0; // initialize to assume the number is not repeated
            vector[i] = rand() % 20 + 1;

            // check if the random number already exists in the vector
            for (int j = 0; j < i; j++)
            {
                if (vector[j] == vector[i])
                {
                    checkRepeated = 1; // set to 1 if the number is repeated
                    break;
                }
            }
        } while (checkRepeated); // repeat until a unique number is generated
    }
    menu();
}

void fillVector3(int vector[], int vector1[], int vector2[], int size)
{
    for (int i = 0; i < size; i++)
    {
        vector[i] = vector1[i];
        vector[i + 10] = vector2[i];
    }
    menu();
}

void fillMatrix(int matrix[][5], int size)
{
    for (int r = 0; r < size; r++)
    {
        for (int c = 0; c < size; c++)
        {
            printf("Matrix[%i, %i]: ", r, c);
            scanf("%i", &matrix[r][c]);
        }
    }
    menu();
}

void printVector(int vector[], int size)
{
    printf("Vector elements: {");
    for (int i = 0; i < size; i++)
    {
        printf("%d", vector[i]);
        if (i < size - 1)
        {
            printf(", ");
        }
    }
    printf("}");
}

void printMatrix(int matrix[][5], int size)
{
    int r, c;

    printf("Matrix elements: \n{\n");
    for (r = 0; r < size; r++)
    {
        for (c = 0; c < size; c++)
        {
            printf("%d\t", matrix[r][c]);
        }
        printf("\n");
    }
    printf("}");
}

问题原因 #

核心问题是递归调用menu()函数：

• 每次调用menu()，都会在栈上创建新的局部数组vector1、vector2、vector3、matrix，这些数组的生命周期仅限于当前menu()函数的栈帧。
• 当你在fillVector1等填充函数完成后调用menu()，原来的menu()栈帧会被销毁，其中填充好的数组数据也随之消失。新调用的menu()里的数组是未初始化的，打印时自然输出随机垃圾值。

解决方案 #

把menu()改成循环结构，去掉递归调用，让填充函数执行完后返回原menu()的循环，这样数组的生命周期会持续到整个程序运行期间（因为数组在menu()的循环内，每次循环复用同一个数组）。

修改后的代码 #

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

void menu();
void fillVector1(int vector[], int size);
void fillVector2(int vector[], int size);
void fillVector3(int vector[], int vector1[], int vector2[], int size);
void fillMatrix(int matrix[][5], int size);
void printVector(int vector[], int size);
void printMatrix(int matrix[][5], int size);

int main()
{
    menu();
    return 0;
}

void menu()
{
    int option;
    // 将数组声明在循环外，保证生命周期覆盖整个菜单交互过程
    int vector1[10];
    int vector2[10];
    int vector3[20];
    int matrix[5][5];

    // 用do-while循环替代递归，实现菜单循环
    do {
        printf("\nARRAYS MENU");
        printf("\n\t1.- Fill Vector 1\n\t2.- Fill Vector 2\n\t3.- Fill Vector 3\n\t4.- Print Vectors\n\t5.- Fill Matrix 4x4\n\t6.- Print Matrix\n\t0.- Close Program\n");
        printf("Select an option: ");
        scanf("%i", &option);

        switch (option)
        {
        case 1:
            fillVector1(vector1, 10);
            break;
        case 2:
            fillVector2(vector2, 10);
            break;
        case 3:
            fillVector3(vector3, vector1, vector2, 10);
            printf("\n");
            printVector(vector3, 20); // 修正原代码打印长度错误
            break;
        case 4:
            printf("\nVector 1: ");
            printVector(vector1, 10);
            printf("\nVector 2: ");
            printVector(vector2, 10);
            printf("\nVector 3: ");
            printVector(vector3, 20);
            break;
        case 5:
            fillMatrix(matrix, 4);
            break;
        case 6:
            printf("\n");
            printMatrix(matrix, 4);
            break;
        case 0:
            printf("\nThanks for using this program. Come back soon!");
            break;
        default:
            printf("\nInvalid option. Select another one.");
            break;
        }
    } while (option != 0); // 直到选择0才退出循环
}

void fillVector1(int vector[], int size)
{
    printf("\nFill it only with numbers between 30 to 70\n");

    for (int i = 0; i < size; i++)
    {
        printf("Vector[%i]: ", i);
        scanf("%i", &vector[i]);

        if (vector[i] < 30 || vector[i] > 70)
        {
            printf("Value out of range. Please enter another number.\n");
            i--; // repeat last (incorrect) index
        }
    }
    // 去掉menu()递归调用，直接返回原menu循环
}

void fillVector2(int vector[], int size)
{
    printf("\nVector filled with random numbers between 1 to 20\n");

    int checkRepeated;

    srand(time(NULL));
    for (int i = 0; i < size; i++)
    {
        // function to avoid repeated number
        do
        {
            checkRepeated = 0; // initialize to assume the number is not repeated
            vector[i] = rand() % 20 + 1;

            // check if the random number already exists in the vector
            for (int j = 0; j < i; j++)
            {
                if (vector[j] == vector[i])
                {
                    checkRepeated = 1; // set to 1 if the number is repeated
                    break;
                }
            }
        } while (checkRepeated); // repeat until a unique number is generated
    }
    // 去掉menu()递归调用
}

void fillVector3(int vector[], int vector1[], int vector2[], int size)
{
    for (int i = 0; i < size; i++)
    {
        vector[i] = vector1[i];
        vector[i + 10] = vector2[i];
    }
    // 去掉menu()递归调用
}

void fillMatrix(int matrix[][5], int size)
{
    printf("\nFill Matrix 4x4:\n");
    for (int r = 0; r < size; r++)
    {
        for (int c = 0; c < size; c++)
        {
            printf("Matrix[%i, %i]: ", r, c);
            scanf("%i", &matrix[r][c]);
        }
    }
    // 去掉menu()递归调用
}

void printVector(int vector[], int size)
{
    printf("Vector elements: {");
    for (int i = 0; i < size; i++)
    {
        printf("%d", vector[i]);
        if (i < size - 1)
        {
            printf(", ");
        }
    }
    printf("}");
}

void printMatrix(int matrix[][5], int size)
{
    int r, c;

    printf("Matrix elements: \n{\n");
    for (r = 0; r < size; r++)
    {
        for (c = 0; c < size; c++)
        {
            printf("%d\t", matrix[r][c]);
        }
        printf("\n");
    }
    printf("}");
}

额外修正点 #

• 原代码中case 3打印vector3时传入的size是10，而vector3实际是20个元素，修改为20以保证完整打印。
• 在菜单和各函数中添加换行，优化输出可读性。

内容的提问来源于stack exchange，提问作者kewvy