c - 这个小 for 循环中的内存泄漏和 valgrind 错误？

Question

我在处理在 valgrind 中生成错误的一小部分代码时遇到了问题。当我注释代码并运行 valgrind 时，我没有遇到任何内存泄漏或错误，所以这个循环应该是原因:

///Print the top users
    const char* str;
    for (int i = 0; i < count; i++) {
        if (FinalArray[i].Score == -1) {
            break;
        }

        int id = UserGetID(user);
        char* name = UserGetName(user);
        int finalID = UserGetID(FinalArray[i].user);
        char* finalName = UserGetName(FinalArray[i].user);

        assert(finalName!= NULL && name !=NULL);
        str = mtmSuggestFriends(id, name, finalID, finalName);

        if (str == NULL) {
            return MAIN_ALLOCATION_FAILED;
        }

//      fprintf(fileOutput, str);
    }

在这个循环之后我简单地返回一个枚举说明成功。

以下是 Valgrind 中的错误:

==8779== Use of uninitialised value of size 8
==8779==    at 0x4037C2: UserGetName (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x401FAC: SuggestFriends (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x402E6D: executeUserCommand (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x40281B: main (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779== 
==8779== Use of uninitialised value of size 8
==8779==    at 0x4037A0: UserGetID (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x401FC8: SuggestFriends (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x402E6D: executeUserCommand (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x40281B: main (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779== 
==8779== Invalid read of size 1
==8779==    at 0x403F1A: mtmSuggestFriends (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x401FEE: SuggestFriends (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x402E6D: executeUserCommand (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x40281B: main (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==  Address 0x9848B4458BB44589 is not stack'd, malloc'd or (recently) free'd
==8779== 
==8779== Process terminating with default action of signal 11 (SIGSEGV)
==8779==  General Protection Fault
==8779==    at 0x403F1A: mtmSuggestFriends (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x401FEE: SuggestFriends (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x402E6D: executeUserCommand (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779==    by 0x40281B: main (in /u1/023/mtm/ex2/RUN/mtm_isocial)
==8779== 
==8779== ERROR SUMMARY: 3 errors from 3 contexts (suppressed: 4 from 1)
==8779== malloc/free: in use at exit: 1,250 bytes in 93 blocks.
==8779== malloc/free: 455 allocs, 362 frees, 10,081 bytes allocated.
==8779== For counts of detected errors, rerun with: -v
==8779== searching for pointers to 93 not-freed blocks.
==8779== checked 122,512 bytes.
==8779== 
==8779== LEAK SUMMARY:
==8779==    definitely lost: 0 bytes in 0 blocks.
==8779==      possibly lost: 0 bytes in 0 blocks.
==8779==    still reachable: 1,250 bytes in 93 blocks.
==8779==         suppressed: 0 bytes in 0 blocks.
==8779== Reachable blocks (those to which a pointer was found) are not shown.
==8779== To see them, rerun with: --show-reachable=yes

ToStringUser 函数返回一个 const char* 的 malloc。所以我不应该担心释放它吗？

知道为什么会这样吗？

我试图在 for 中使用此代码释放 str，但我不断收到相同的错误和相同数量的内存泄漏:

free((char*) str); OR free((void*) str);

这是 User 和 getID 和 getName 的结构:

struct User_t {
    char *Name;
    int ID;
    int Birth;
};
int UserGetID(User user) {
    return user->ID;
}
char* UserGetName(User user) {
    return user->Name;
}

在循环之前我用这个初始化一个新用户:

User user = FindUserPointer(setUser, id);

使用的函数是这样的:

static User FindUserPointer(Set users, int ID) {
        assert(users!=NULL);
    User tmpUser = UserCreate("temp", ID, 99);
    if (tmpUser == NULL) {
        return NULL;
    }
    SET_FOREACH(User,Itrator1,users) {
        if (UserCompare(tmpUser, Itrator1) == 0) {
            UserFree(tmpUser);
            return Itrator1;
        }
    }
    UserFree(tmpUser);
    return NULL;
}

Answer 1

Valgrind 并不是在提示泄漏 - 它是在提示您正在读取未初始化的内存并取消引用无效指针(无效指针 deref 正在使程序崩溃 - 至少在 Valgrind 下是这样)。

我们需要查看 UserGetID() 和 UserGetName() 才能确定其中的错误(但这可能还不够)。

根据您的评论，mtmSuggestFriends 是一个您没有源代码的目标文件，我的猜测是 UsetGetID() 和/或 UserGetName () 将无效指针传递给 mtmSuggestFriends。