[英]Memory leak and valgrind errors in this small for loop?
我在这部分代码中遇到了麻烦,该代码在valgrind中生成错误。 当我注释代码并运行valgrind时,我没有收到任何内存泄漏或错误,因此此循环应为原因:
///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);
}
在此循环之后,我只返回一个声明成功的枚举。
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
函数ToStringUser返回const char *的malloc。因此,我不必担心释放它吗?
知道为什么会这样吗?
我尝试使用for中的此代码释放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的结构以及getID和getName:
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,我以此初始化一个新用户:
User user = FindUserPointer(setUser, id);
使用的功能是这样的:
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;
}
Valgrind并不是在抱怨泄漏-它是在抱怨您正在读取未初始化的内存并取消引用无效的指针(无效的指针deref导致程序崩溃-至少在Valgrind下)。
我们需要查看UserGetID()
和UserGetName()
才能确定其中的错误(但是可能还不够)。
根据您的评论mtmSuggestFriends
是您没有源的目标文件,我猜测UsetGetID()
和/或UserGetName()
将无效的指针传递给mtmSuggestFriends
。
首先,您要传入一个未分配的指针user
。 然后,从UserGetID()
调用的SuggestFriends()
函数将这个充满随机性的垃圾指针用作真实指针,从而导致无效读取( SEGV
)
您可能会发现,设置“警告为错误”(gcc上的-Werr
)可能会向您显示您在做不可预测的事情。
struct User_t {
char *Name;
int ID;
int Birth;
};
int UserGetID(User user) {
return user->ID;
}
... User
定义在哪里?
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