Question

我是C语言的初学者，这是我第一个使用malloc（）函数的程序。我认为使用这个函数可能会有一些问题。我想使用一个数组（cyclelength），其中将放置一系列数字（用户输入）的解决方案。所以数组大小取决于用户所以我使用了malloc（）。但程序崩溃了。这是我的代码：

#include<stdio.h>
#include<stdlib.h>
int main()
{
    int x,y,num,count,p,k;
    for(;;){
        printf("enter first integer. must be between 1 and 100000\n");
        scanf("%d", &x);
        printf("enter second integer. must be between 1 and 100000. must not equal the first integer.\n");
        scanf("%d", &y);
        if(x>=1 && x<100000 && y>=1 && y<100000 && x!=y){
            break;
        }
        else{
            printf("try the whole process again\n");
        }
    }
    if (x<y){
        int j;
        j=y;
        y=x;
        x=j;
    } //making x always greater than y
    int *cyclelength=malloc(5000*sizeof(int));
    if (NULL==cyclelength){
        printf("process aborted");
    }
    else{
        /*solution part for the range of number. and solution for each number  put into cyclelength.*/
        num=y;
        while(num<=x){
            p=1;
            k=num;
            while(k!=1){
                if(k%2==0)
                    k=k/2;
                else
                    k=3*k+1;
                p+=1;
                }
            count=0;
            cyclelength[count]=p;
            num+=1;
            count+=1;
        }
        free(cyclelength);
        cyclelength=NULL;
    }
    int c=0;
    int max=cyclelength[c];
    for(;c<x-y;c+=1){
        if(max<cyclelength[c+1]){
            max=cyclelength[c+1];
        }
    }
    printf("%d,%d,%d",x,y,max);
    return 0;
}

Answer 1

您正在调用free(cyclelength)和然后访问它指向的内存（或者更确切地说，它指向的内存）。

（您的错误处理可能会有所改善;您打印"process aborted"，然后继续处理。）

Answer 2

您在cyclelength之后使用free并将其设置为NULL：

        free(cyclelength);
        cyclelength=NULL;
    }
    int c=0;
    int max=cyclelength[c];
    for(;c<x-y;c+=1){
        if(max<cyclelength[c+1]){
            max=cyclelength[c+1];
        }

这是未定义的行为，可能会崩溃。

Answer 3

你正在使用cyclelength，因此你的程序崩溃了试试这个：

#include<stdio.h>
#include<stdlib.h>
int main()
{
    int x,y,num,count,p,k;
    for(;;){
        printf("enter first integer. must be between 1 and 100000\n");
        scanf("%d", &x);
        printf("enter second integer. must be between 1 and 100000. must not equal the first integer.\n");
        scanf("%d", &y);
        if(x>=1 && x<100000 && y>=1 && y<100000 && x!=y){
            break;
        }
        else{
            printf("try the whole process again\n");
        }
    }
    if (x<y){
        int j;
        j=y;
        y=x;
        x=j;
    } //making x always greater than y
    int *cyclelength=(int *)malloc(5000*sizeof(int));
    if (NULL==cyclelength){
        printf("process aborted");
    }
    else{
        /*solution part for the range of number. and solution for each number  put into cyclelength.*/
        num=y;
        while(num<=x){
            p=1;
            k=num;
            while(k!=1){
                if(k%2==0)
                    k=k/2;
                else
                    k=3*k+1;
                p+=1;
                }
            count=0;
            cyclelength[count]=p;
            num+=1;
            count+=1;
        }        
        // don't assign null to cyclelength
        //cyclelength=NULL;
    }
    int c=0;
    int max=cyclelength[c];
    for(;c<x-y;c+=1){
        if(max<cyclelength[c+1]){
            max=cyclelength[c+1];
        }
    }
    printf("%d,%d,%d",x,y,max);
    // free here
    free(cyclelength);
    return 0;
}

malloc函数在C程序中无法正常工作。程序崩溃了

3 个答案: