Question

大家好，我试图完成一个涉及我自己的异常的代码，但我在运行valgrind时遇到了一些错误。错误不会一直发生，通常只是第一次尝试。似乎异常的字符串给出了麻烦，但是当抛出异常时它仍会打印出来......任何可能导致问题的想法？你的时间：）

       #include <iostream>
        #include <sstream>
       #include <exception>
       using namespace std;
       class wrongMessageIndex:public exception{
public:
    int index;
public:
    wrongMessageIndex(int& num){index=num;};
    virtual const char* what() const throw(){
        stringstream s;
        string k="Wrong message index: ";
        s<<k<<index;
        return (s.str().c_str());
    }

};
class NoUserInSystem:public exception{
public:
    string user;
public:
    NoUserInSystem(string name){user=name;};
    virtual const char* what() const throw(){
        string k=user;
                k+=": no such user ";
        return (k.c_str());
    }
    virtual ~NoUserInSystem() throw(){}
};
class MemoreyFail:public exception{
public:
    virtual const char* what() const throw(){
        return ("Unable to create new message or write in the right file");
    }
    virtual ~MemoreyFail() throw(){}
};

引发异常的部分

string user="";
int checker=0;
while(!file.eof()){
    getline(file,user);
    if(strcmp(user.c_str(),to_who.c_str())==0)
    {
        checker=-1;
    }
}
if(checker!=-1||strcmp(this->nameOfUser.c_str(),to_who.c_str())==0){
throw NoUserInSystem(to_who);
}

这是发现异常的地方：

try{
            this->sendSingleMessage();
        }
        catch(exception& e){
            cout<<e.what()<<endl;
        }

这里有一些我得到的错误

Welcome zamri , you have 2 new messages.
Eva would like to update you that:
What would you like to do?
(1) See the list of all messages 
(2) Read the next new message 
(3) Read a message by index number 
(4) Read a complete correspondence 
(5) Write a new message 
(6) Write a new mass-message 
(7) Quit 
Please type you choice 
5
To:tony
==2945== Invalid read of size 1
==2945==    at 0x402C658: strlen (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2945==    by 0x40CAC2D: std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x804A144: main (in /home/ise/Ass4/myMs)
==2945==  Address 0x4342834 is 12 bytes inside a block of size 32 free'd
==2945==    at 0x402ACFC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2945==    by 0x40D699A: std::string::_Rep::_M_destroy(std::allocator<char> const&) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x804D2A2: RegularUser::showMenue() (in /home/ise/Ass4/myMs)
==2945==    by 0x804A144: main (in /home/ise/Ass4/myMs)
==2945== 
==2945== Invalid read of size 1
==2945==    at 0x402C663: strlen (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2945==    by 0x40CAC2D: std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x804A144: main (in /home/ise/Ass4/myMs)
==2945==  Address 0x4342835 is 13 bytes inside a block of size 32 free'd
==2945==    at 0x402ACFC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2945==    by 0x40D699A: std::string::_Rep::_M_destroy(std::allocator<char> const&) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x804D2A2: RegularUser::showMenue() (in /home/ise/Ass4/myMs)
==2945==    by 0x804A144: main (in /home/ise/Ass4/myMs)
==2945== 
==2945== Invalid read of size 1
==2945==    at 0x41B868B: _IO_file_xsputn@@GLIBC_2.1 (fileops.c:1330)
==2945==    by 0x41AD757: fwrite (iofwrite.c:45)
==2945==    by 0x40C9075: __gnu_cxx::stdio_sync_filebuf<char, std::char_traits<char> >::xsputn(char const*, int) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x40CA9AA: std::basic_ostream<char, std::char_traits<char> >& std::__ostream_insert<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*, int) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x40CAC3D: std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x804A144: main (in /home/ise/Ass4/myMs)
==2945==  Address 0x4342846 is 30 bytes inside a block of size 32 free'd
==2945==    at 0x402ACFC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2945==    by 0x40D699A: std::string::_Rep::_M_destroy(std::allocator<char> const&) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x804D2A2: RegularUser::showMenue() (in /home/ise/Ass4/myMs)
==2945==    by 0x804A144: main (in /home/ise/Ass4/myMs)
==2945== 
==2945== Invalid read of size 1
==2945==    at 0x41B869F: _IO_file_xsputn@@GLIBC_2.1 (fileops.c:1330)
==2945==    by 0x41AD757: fwrite (iofwrite.c:45)
==2945==    by 0x40C9075: __gnu_cxx::stdio_sync_filebuf<char, std::char_traits<char> >::xsputn(char const*, int) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x40CA9AA: std::basic_ostream<char, std::char_traits<char> >& std::__ostream_insert<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*, int) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x40CAC3D: std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x804A144: main (in /home/ise/Ass4/myMs)
==2945==  Address 0x4342845 is 29 bytes inside a block of size 32 free'd
==2945==    at 0x402ACFC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2945==    by 0x40D699A: std::string::_Rep::_M_destroy(std::allocator<char> const&) (in /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16)
==2945==    by 0x804D2A2: RegularUser::showMenue() (in /home/ise/Ass4/myMs)
==2945==    by 0x804A144: main (in /home/ise/Ass4/myMs)
==2945==

Answer 1

 return (s.str().c_str());

返回指向流对象缓冲区临时副本的内部缓冲区的第一个元素的指针。所以what()完成后，这个指针就会悬空。

基本上是同样的问题：

return (k.c_str());

将指针返回到本地字符串k的缓冲区中，该字符串将立即超出范围。

要解决此问题，只需删除此指针业务，只需按值返回std::string即可。

抛出异常时valgrind中的错误

1 个答案: