Question

我使用valgrind使用选项track-origins=yes来调试我的代码并遇到了这个错误。

$ valgrind --track-origins=yes ./frgtnlng < in > out
==7098== 
==7098== Conditional jump or move depends on uninitialised value(s)
==7098==    at 0x4C2F1BC: strcmp (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==7098==    by 0x400857: main (frgtnlng.c:24)
==7098==  Uninitialised value was created by a stack allocation
==7098==    at 0x40064C: main (frgtnlng.c:9)
==7098== 
==7098== Conditional jump or move depends on uninitialised value(s)
==7098==    at 0x40085A: main (frgtnlng.c:24)
==7098==  Uninitialised value was created by a stack allocation
==7098==    at 0x40064C: main (frgtnlng.c:9)

第9行是：

scanf("%d", &t);

我不明白这是如何导致问题的。

frgtnlng.c：

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

int main(void)
{
    int t, n, k, l, i, j, z, out[100];
    char f[5][100], m[5][50][50];

    scanf("%d", &t);
    while (t--) {
        for (i = 0; i < 100; i++)
            out[i] = 0;
        scanf("%d%d", &n, &k);
        for (i = 0; i < n; i++)
            scanf("%s", f[i]);
        for (i = 0; i < k; i++) {
            scanf("%d", &l);
            for (j = 0; j < l; j++)
                scanf("%s", m[i][j]);
        }
        for (i = 0; i < k; i++)
            for (j = 0; j < l; j++)
                for (z = 0; z < n; z++) {
                    if (strcmp(m[i][j], f[z]) == 0)
                        out[z] = 1;
                }
        for (i = 0; i < n; i++) {
            if (out[i])
                printf("YES ");
            else
                printf("NO ");
        }
        printf("\n");
    }
    return 0;
}

在：

2
3 2
piygu ezyfo rzotm
1 piygu
6 tefwz tefwz piygu ezyfo tefwz piygu
4 1
kssdy tjzhy ljzym kegqz
4 kegqz kegqz kegqz vxvyj

Answer 1

valgrind的行号已关闭：它应该为分配行号报告7而不是9。然而，错误行24是正确的 - 问题在于：

if (strcmp(m[i][j], f[z]) == 0)

问题是j从0循环到l-1，包括l，但l是在 last 迭代中设置的任何内容。读取2D数组的循环，即4.这就是为什么每次它到达数组中的一行时，从数组的未初始化部分读取的数据少于4个。

修复方法是通过使l[5]成为数组l[i]并在两个循环中使用for (i = 0; i < k; i++) { scanf("%d", &l[i]); for (j = 0; j < l[i]; j++) scanf("%s", m[i][j]); } for (i = 0; i < k; i++) for (j = 0; j < l[i]; j++) for (z = 0; z < n; z++) { if (strcmp(m[i][j], f[z]) == 0) out[z] = 1; }来单独存储各行的长度：

currentUser

未初始化的值是由堆栈分配创建的 - valgrind

1 个答案: