c++ - 内存堆和泄漏总结

Question

我正在通过 matrix 提交我的学校研讨会，我收到关于内存泄漏的警告，但是，当我编译它并通过 g++ 命令或 VS 运行时，它没有显示任何警告或错误。

那是提交的开始

Checking due date:
ON TIME.

Compiling:
g++ -Wall -std=c++11 -o ws utils.o School.cpp schoolTester.cpp Subject.cpp utils.cpp 2> errors.txt

Compile result:
Success! no errors or warnings...

Testing execution:
READ THE FOLLOWING CAREFULLY!
I am about to execute the tester and capture the output in "student_output.txt"
Please enter the values carefuly and exactly as instructed.
Press <ENTER> to start...
Script started, file is student_output.txt
==203824== Memcheck, a memory error detector
==203824== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==203824== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==203824== Command: ws
==203824==
Begin Testing the Program!
--------------------------

Please enter the name of the school:
>

当我运行代码时，我得到了这个摘要

------------------------
End Testing the Program!
==209192==
==209192== HEAP SUMMARY:
==209192==     in use at exit: 200 bytes in 1 blocks
==209192==   total heap usage: 9 allocs, 8 frees, 366 bytes allocated
==209192==
==209192== LEAK SUMMARY:
==209192==    definitely lost: 200 bytes in 1 blocks
==209192==    indirectly lost: 0 bytes in 0 blocks
==209192==      possibly lost: 0 bytes in 0 blocks
==209192==    still reachable: 0 bytes in 0 blocks
==209192==         suppressed: 0 bytes in 0 blocks
==209192== Rerun with --leak-check=full to see details of leaked memory
==209192==
==209192== For counts of detected and suppressed errors, rerun with: -v
==209192== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
Script done, file is student_output.txt

这是代码本身:

学校.cpp

namespace sdds {

    School Sch;
    Subject Sub[5];

    void read(School& Sch) {
        Sch.m_name = new char[30];
        char name [61];
        cout << "Please enter the name of the school:\n> ";
        read( name, 61, "Name is too long, only 60 characters allowed!\nRedo Entry: ");

        strcpy(Sch.m_name, name);
        cout << "Please enter the number of subjects offered by " << Sch.m_name << ": ";
        Sch.m_noOfSubjects = new int[50];
        read(*Sch.m_noOfSubjects, 2, 50, "Invalid Number of subjects, 2<=ENTRY<=50\nRedo Entry: ");
        Sch.m_subjects = new int[*Sch.m_noOfSubjects];

        for (int i = 0; i < *Sch.m_noOfSubjects; i++) {
            cout << i+1 << ") ------------------------------" << endl;
            read(Sub[i]);


        }
    }

    int report(const School&Sch) {
        int totalEnr = 0;

        cout << Sch.m_name<<endl;
        cout << "Subject Enrollments" << endl;

        for (int i = 0; i < *Sch.m_noOfSubjects; i++) {
            totalEnr += report(Sub[i]);



        }
        cout << "Total enrollment: " << totalEnr;
        return totalEnr;
    }

    void freeMem(School& Sch) {

        delete [] Sch.m_name;
        Sch.m_name = NULL;

        for (int i = 0; i < *Sch.m_noOfSubjects; i++) {
            freeMem (Sub[i]);
        }

        delete [] Sch.m_subjects;
        Sch.m_subjects = NULL;
    }

}

主题.cpp

namespace sdds {






    void read(char* str) {

        cout << "Enter subject name: ";

        read(str, 71, "Name is too long, only 70 characters allowed!\nRedo Entry : ");

    }

    void read(int& noofSections) {

        cout << "Enter number of sections: ";

        read(noofSections, 0, 11, "Invalid Number of sections, 1<=ENTRY<=10\nRedo Entry: ");

    }

    void read(int noOfStdsInSecs[], int noOfSections) {
                cout << "Enter the number of students in each one of the " << noOfSections << " sections:" << endl;


        for (int i = 0; i < noOfSections; i++) {

            cout << i+1 << ": ";
            read(noOfStdsInSecs[i], 5, 35, "Invalid Number of students, 5<=ENTRY<=35\nRedo Entry: ");

        }


    }

    void read(Subject& Sub) {


        char subjectName[71];
        read(subjectName);
        Sub.m_subjectName = new char[50];
        strcpy(Sub.m_subjectName, subjectName);

        Sub.m_noOfSections = new int;
        read(*Sub.m_noOfSections);


        Sub.m_noOfStdsInSecs = new int [*Sub.m_noOfSections];
        read(Sub.m_noOfStdsInSecs, *Sub.m_noOfSections);

    }

void freeMem(Subject& Sub) {

        delete[] Sub.m_subjectName;
        Sub.m_subjectName = NULL;
        delete Sub.m_noOfSections;
        Sub.m_noOfSections = NULL;
        delete [] Sub.m_noOfStdsInSecs;
        Sub.m_noOfStdsInSecs = NULL;

    }

更新:将 Sch.m_noOfSubjects 变成一个 int 后，我​​一直得到相同的堆摘要，但现在它确实说一切都很好，但正因为如此，我无法提交它，因为我的输出和提交矩阵脚本的输出不匹配。有没有办法以某种方式将其关闭？

------------------------
End Testing the Program!
==1821==
==1821== HEAP SUMMARY:
==1821==     in use at exit: 0 bytes in 0 blocks
==1821==   total heap usage: 8 allocs, 8 frees, 166 bytes allocated
==1821==
==1821== All heap blocks were freed -- no leaks are possible
==1821==
==1821== For counts of detected and suppressed errors, rerun with: -v
==1821== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
Script done, file is student_output.txt

Checking output:
In line number 33 of your output:
The output should be:

^
But your output is:
[38;5;9m------------------------
^

Answer 1

泄密只是一个插曲

应该完全没有泄漏。正确的东西正在被释放，错误在于不必要地分配了一件东西。

看看如何m_noOfSubjects在分配数组后使用:

read(*Sch.m_noOfSubjects, 2, 50, "Invalid Number of subjects, 2<=ENTRY<=50\nRedo Entry: ");

和

Sch.m_subjects = new int[*Sch.m_noOfSubjects];

和

for (int i = 0; i < *Sch.m_noOfSubjects; i++) 

全部使用一个值:第一个。这不是数组的行为。这是单个 int 的行为.

m_noOfSubjects不应是指向数组或 int 的指针或类似的东西。它应该只是一个愚蠢的，ol' int .

在School的定义，替换

int * m_noOfSubjects;

与

int m_noOfSubjects;

然后删除分配

Sch.m_noOfSubjects = new int[50];

最后消除所有的取消引用。例如

read(*Sch.m_noOfSubjects, 2, 50, "Invalid Number of subjects, 2<=ENTRY<=50\nRedo Entry: ");
     ^ remove

和

Sch.m_subjects = new int[*Sch.m_noOfSubjects];
                         ^ remove

和

for (int i = 0; i < *Sch.m_noOfSubjects; i++) 
                    ^ remove

跟踪和避免内存泄漏的思考过程(原答案)

报告说丢失了一个 200 字节的 block 。您可以查看代码以查找分配 200 字节的位置并进行更仔细的调查。例如，如果 int是 32 位，Sch.m_noOfSubjects = new int[50];符合要求 32 位 = 4 字节。 4*50 = 200。

让我们关注m_noOfSubjects通过并确保它得到正确管理。

一个 CTRL+F 之后...

果然我找不到delete的 m_noOfSubjects给定代码中的任何位置。

我们如何解决这个问题？ std::vector<int> 应该去处理这样的问题。 vector为您处理从分配到取消分配的所有资源管理，并同时正确处理复制和分配。

也就是说，我怀疑这个作业应该教给你的是 RAII .在这种情况下，您要做的是向 School 添加构造函数和析构函数(以及复制构造函数和赋值运算符，因为 if you need a destructor, you almost always need special code to handle copying)。类(class)。不要分配 School一些资源read免费功能，不会对 School 的健康和幸福产生任何影响类(class)。 School应该通过在其构造函数中或在其自己的输入法中分配存储来寻找自己。后来，析构函数保证所有School的资源在 School 后立即释放超出范围。您所要做的就是确保 School超出范围。