c - 关闭文件时出现"Double free or corruption(out)"？

Question

我编写了一段代码来练习各种参数(文件、动态二维数组、传递函数指针等)，所以不要介意某些段落看起来毫无用处。在运行时，如果我输入超过 3 行，程序就会崩溃，终端显示“双重释放或损坏(出)”，然后创建核心转储。该错误应该发生在 foo2 中的 fclose(fp) 上。

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

void foo1(int *);
void foo2(int*,int,int**,FILE*);
void readfoo(FILE *, int **, int);

int main(void)
{
    FILE *fp;
    int **a, i, j, r, c, *pr, *pn, *pc;
    pc = &c;
    pr = &r;
    foo1(pr);
    a = malloc(r*sizeof(int));
    foo2(pc,r,a,fp);
    if((fp = fopen("column.txt", "r")) == NULL)
    {
        fprintf(stderr, "Error, can't open \"column.txt\"");
        exit(1);
    }
    for(i=0;i<r;i++)
    {
        fscanf(fp,"%d", &c);
        for(j=0; j<c; j++)
        {
            fprintf(stdout, "insert line %d column %d -> ", i+1, j+1);
            fscanf(stdin, "%d", &a[i][j]);
        }
    }
    if(fclose(fp) != 0)
    {
        fprintf(stderr, "Error, can't close \"column.txt\"");
        exit(1);
    }
    readfoo(fp,a,r);
    remove("column.txt");
    return(0);
}

void foo1(int *r)
{
    fprintf(stdout, "how many lines ? -> ");
    fscanf(stdin, "%d", r);
}

void foo2(int *c, int r, int **a, FILE *fp)
{
    int i,j, act_c;
    if((fp = fopen("column.txt", "w")) == NULL)
    {
        fprintf(stderr, "Error, can't open \"column.txt\"");
        exit(1);
    }
        for(i=0;i<r;i++)
    {
        fprintf(stdout, "how many columns for line %d? -> ", i+1);
        fscanf(stdin, "%d", c);
        fprintf(fp,"%d\n", *c);
        a[i] = malloc((*c)*sizeof(int));
    }
    if(fclose(fp) != 0)
    {
        fprintf(stderr, "Error, can't close \"column.txt\"");
        exit(1);
    }
}

void readfoo(FILE *fp, int **a, int r)
{
    int c, i, j;
    fprintf(stdout, "printing the matrix... \n");
    if((fp = fopen("column.txt", "r")) == NULL)
    {
        fprintf(stderr, "Error, can't open \"column.txt\"");
        exit(1);
    }
    for(i=0;i<r;i++)
    {
        fscanf(fp,"%d", &c);
        for(j=0; j<c; j++)
        {
            fprintf(stdout, "%d ", a[i][j]);
        }
        fprintf(stdout, "\n");
    }
    if(fclose(fp) != 0)
    {
        fprintf(stderr, "Error, can't close \"column.txt\"");
        exit(1);
    }
}

Answer 1

在main()中你会这样做

 a = malloc(r*sizeof(int));

应该是错误的

 a = malloc(r*sizeof(int *));

如果您为 a[i] 赋值，则会调用 UB，这可能是崩溃的真正原因