[英]C++ Classes not initialized properly
I am working on a programming assignment for a class and am getting a really weird problem. 我正在为一个班级安排编程任务,并且遇到了一个非常奇怪的问题。 The technical problem is that I'm getting a seg fault when I try to do anything to a particular vector, but the object it's in and the object that object is in is also acting really weird. 技术问题是,当我尝试对特定向量执行任何操作时遇到段错误,但是该对象所在的对象以及该对象所在的对象的行为也确实很奇怪。 I suspect that it may be a simple syntax error that I don't know how best to solve, so let's start with that. 我怀疑这可能是一个简单的语法错误,我不知道如何最好地解决,所以让我们开始吧。 If this syntax is invalid or only semi-valid, you probably don't need to read the rest (unless changing it doesn't work). 如果此语法无效或仅是半有效的,则可能不需要读取其余语法(除非更改它不起作用)。
Anyway, here's the code I'm concerned about (in the addRel
function of my Database.h file): 无论如何,这是我关注的代码(在我的Database.h文件的addRel
函数中):
#ifndef DATABASE_H_
#define DATABASE_H_
#include "Parser.h"
#include "Relation.h"
#include <map>
class Database {
private:
std::map<std::string, Relation> relations;
std::stringstream out;
public:
Database() {}
~Database() {}
Relation* addRel(std::string RelName) {
Relation* tmp = getRel(RelName);
if(tmp == NULL) {
relations.insert(std::pair<std::string, Relation> (RelName, Relation(RelName))); //Is this a valid approach?
tmp = getRel(RelName);
}
return tmp;
}
bool findRel(std::string RelName) {return getRel(RelName) != NULL;}
Relation* getRel(std::string RelName) {return &relations.find(RelName)->second;}
...
};
I don't exactly want to create a Relation
object in that function, but I need to have a Relation
object to pass into relations.insert
, so I just called the constructor for Relation in the function parameters. 我并不想在该函数中创建一个Relation
对象,但是我需要有一个Relation
对象才能传递给relations.insert
,因此我只是在函数参数中调用了Relation的构造函数。 If there's a better way to do this, that may be the cause of my grief, else I fear the worst, so here's a bunch of code and terminal output: 如果有更好的方法可以做到这一点,那可能是让我悲伤的原因,否则我会担心最坏的情况,因此这是一堆代码和终端输出:
Tuple.h (no .cpp): Tuple.h(无.cpp):
#ifndef TUPLE_H_
#define TUPLE_H_
#include <string>
#include <vector>
class Tuple : public std::vector<std::string> {};
//This approach was specifically encouraged by my instructor
#endif
Scheme.h (no .cpp): Scheme.h(无.cpp):
#ifndef SCHEME_H_
#define SCHEME_H_
#include "Tuple.h"
#include <utility>
class Scheme {
private:
std::vector<std::string> attrs;
std::string test; //for testing purposes
public:
Scheme() {
attrs.clear();
test = "This is a scheme.";
}
~Scheme() {}
void addAttr(std::string newAttr) {attrs.push_back(newAttr);}
std::vector<std::string>* getAttrs() {return &attrs;}
void clear() {attrs.clear();}
std::string getTest() {return test;}
};
#endif
Relation.h (.cpp not relevant): Relation.h(.cpp不相关):
#ifndef RELATION_H_
#define RELATION_H_
#include "Scheme.h"
#include "Tuple.h"
#include <set>
class Relation {
private:
std::string name;
Scheme idents;
...
public:
Relation(std::string newName) : name(newName) {}
~Relation() {}
std::string getName() {return name;}
Scheme* getScheme() {return &idents;}
...
};
#endif
Database.h (.cpp excerpt below): Database.h(下面的.cpp摘录):
#ifndef DATABASE_H_
#define DATABASE_H_
#include "Parser.h"
#include "Relation.h"
#include <map>
class Database {
private:
std::map<std::string, Relation> relations;
std::stringstream out;
public:
Database() {}
~Database() {}
Relation* addRel(std::string RelName) {
Relation* tmp = getRel(RelName);
if(tmp == NULL) {
relations.insert(std::pair<std::string, Relation> (RelName, Relation(RelName))); //Is this a valid approach?
tmp = getRel(RelName);
}
return tmp;
}
bool findRel(std::string RelName) {return getRel(RelName) != NULL;}
Relation* getRel(std::string RelName) {return &relations.find(RelName)->second;}
...
};
#endif
Database.cpp (the most interesting file): Database.cpp(最有趣的文件):
#include "Database.h"
#include <iostream>
using namespace std;
void Database::evalSchemes(vector<Predicate> schemes) {
out << "Scheme Evaluation\n\n";
for(unsigned int i = 0; i < schemes.size(); i++) {
string name = schemes[i].getName();
Relation* trel = addRel(name);
Scheme* tsch = trel->getScheme();
cout << "\nEvaluating scheme " << name << "\ni = " << i
<< "\ntrel is " << trel->getName() << "\ntsch = " << tsch
<< "\nTest = " << tsch->getTest() << "\n";
tsch->clear(); //Segfaults here if this line is present
std::vector<Parameter> tvec = schemes[i].getVector();
for(unsigned int j = 0; j < tvec.size(); j++) {
vector<string>* tattrs = tsch->getAttrs();
string new_attr = tvec[j].getValue();
cout << "\n\tAdding attribute " << new_attr << "\n\tj = " << j
<< "\n\tVector size = " << tattrs->size() << "\n";
tsch->addAttr(new_attr); //Segfaults here otherwise
}
}
}
...
Main.cpp: Main.cpp的:
#include "Scanner.h"
#include "Parser.h"
#include "Database.h"
#include <iostream>
using namespace std;
int main(int argc, char* argv[]) {
if(argc < 3) {
cout << "\nIncorrect program usage.\nPlease provide input and output file names.\n";
return 0;
}
else {
Scanner mainScanner(argv[1]);
Parser mainParser;
Database mainDatabase;
mainScanner.scanAll();
mainParser.importVector(mainScanner.getVector());
mainParser.parseAll();
DatalogProgram mainProg = mainParser.getProgram();
//Everything up to this point works just fine
mainDatabase.evalSchemes(mainProg.getSchemes()); //Segfaults during this function
mainDatabase.evalFacts(mainProg.getFacts());
mainDatabase.evalQueries(mainProg.getQueries());
mainDatabase.output(argv[2]);
return 0;
}
}
And here's the output from the program. 这是程序的输出。 I'm running within gdb in Ubuntu 14.04 and ZSH, using g++ to compile, including the output of a backtrack. 我正在Ubuntu 14.04和ZSH中的gdb中运行,使用g ++进行编译,包括回溯的输出。 The second one has more information, so I've commented on the cout results of that program. 第二个有更多信息,因此我对该程序的提示结果进行了评论。
If I attempt to clear the vector before modifying it: 如果我尝试在修改向量之前将其清除:
(gdb) run in30.txt act30.txt
Starting program: /home/stephen/Dropbox/Code/CS_236/Lab3-Database/v1.0.1 in30.txt act30.txt
Evaluating scheme SK
i = 0
trel is @���� ����X����������� �����������������������������������
tsch = 0x7fffffffd878
Test = S
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7b90350 in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string() ()
from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
(gdb) bt
#0 0x00007ffff7b90350 in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string() ()
from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#1 0x000000000040ac7a in std::_Destroy<std::string> (__pointer=0x0) at /usr/include/c++/4.8/bits/stl_construct.h:93
#2 0x0000000000409838 in std::_Destroy_aux<false>::__destroy<std::string*> (__first=0x0,
__last=0x7ffff7dc04e0 <vtable for std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >+64>)
at /usr/include/c++/4.8/bits/stl_construct.h:103
#3 0x00000000004070aa in std::_Destroy<std::string*> (__first=0x0,
__last=0x7ffff7dc04e0 <vtable for std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >+64>)
at /usr/include/c++/4.8/bits/stl_construct.h:126
#4 0x00000000004056c3 in std::_Destroy<std::string*, std::string> (__first=0x0,
__last=0x7ffff7dc04e0 <vtable for std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >+64>)
at /usr/include/c++/4.8/bits/stl_construct.h:151
#5 0x0000000000405ab8 in std::vector<std::string, std::allocator<std::string> >::_M_erase_at_end (this=0x7fffffffd878, __pos=0x0)
at /usr/include/c++/4.8/bits/stl_vector.h:1352
#6 0x0000000000404688 in std::vector<std::string, std::allocator<std::string> >::clear (this=0x7fffffffd878)
at /usr/include/c++/4.8/bits/stl_vector.h:1126
#7 0x00000000004038c8 in Scheme::clear (this=0x7fffffffd878) at Scheme.h:19
#8 0x0000000000401f81 in Database::evalSchemes (this=0x7fffffffd840, schemes=std::vector of length 1, capacity 1 = {...})
at Database.cpp:15
#9 0x000000000040c57f in main (argc=3, argv=0x7fffffffe238) at Main.cpp:26
(gdb)
And here's what happens if I comment that line out: 如果我将这一行注释掉,将会发生以下情况:
(gdb) run in30.txt act30.txt
Starting program: /home/stephen/Dropbox/Code/CS_236/Lab3-Database/v1.0.1 in30.txt act30.txt
Evaluating scheme SK //this is normal
i = 0 //this is normal
trel is @���� ����X����������� ����������������������������������� //should be the relation's name
tsch = 0x7fffffffd878 //memory address, just to make sure it isn't NULL
Test = S //should be "This is a scheme."
Adding attribute A //this is normal
j = 0 //this is normal
Vector size = 17592168972444 /should be 0; I haven't done anything with this vector yet
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7b9146f in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&) ()
from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
(gdb) bt
#0 0x00007ffff7b9146f in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&) ()
from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#1 0x00000000004098ca in __gnu_cxx::new_allocator<std::string>::construct<std::string<std::string const&> > (this=0x7fffffffd878,
__p=0x7ffff7dc04e0 <vtable for std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >+64>)
at /usr/include/c++/4.8/ext/new_allocator.h:120
#2 0x00000000004070ca in std::allocator_traits<std::allocator<std::string> >::_S_construct<std::string<std::string const&> >(std::allocator<std::string>&, std::allocator_traits<std::allocator<std::string> >::__construct_helper*, (std::string<std::string const&>&&)...) (__a=..., __p=0x7ffff7dc04e0 <vtable for std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >+64>)
at /usr/include/c++/4.8/bits/alloc_traits.h:254
#3 0x000000000040572e in std::allocator_traits<std::allocator<std::string> >::construct<std::string<std::string const&> >(std::allocator<std::string>&, std::string<std::string const&>*, (std::string<std::string const&>&&)...) (__a=...,
__p=0x7ffff7dc04e0 <vtable for std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >+64>)
at /usr/include/c++/4.8/bits/alloc_traits.h:393
#4 0x0000000000404528 in std::vector<std::string, std::allocator<std::string> >::push_back (this=0x7fffffffd878, __x="A")
at /usr/include/c++/4.8/bits/stl_vector.h:905
#5 0x0000000000403893 in Scheme::addAttr (this=0x7fffffffd878, newAttr="A") at Scheme.h:17
#6 0x000000000040207a in Database::evalSchemes (this=0x7fffffffd840, schemes=std::vector of length 1, capacity 1 = {...})
at Database.cpp:22
#7 0x000000000040c559 in main (argc=3, argv=0x7fffffffe238) at Main.cpp:26
(gdb)
Since the trel
line doesn't quite look like it does in the terminal, here's a screen capture of that area of the output: 由于trel
线看起来trel
终端中的线,因此以下是该输出区域的屏幕截图:
I would really appreciate absolutely any insight you can offer, as I'm at a complete loss, in part because I just don't know how to phrase the first mini-question into an effective Google search. 我非常感谢您提供的任何见解,因为我完全不知所措,部分原因是我不知道如何在有效的Google搜索中表达第一个小问题。 And if all you can answer is the first bit, that would still be absolutely fantastic. 如果您能回答的只是第一点,那绝对是很棒的。
My apologies if I'm way off, but I believe one problem may be in Database::getRel: 我很抱歉,如果我走了,但我相信一个问题可能出在Database :: getRel:
return &relations.find(RelName)->second;
The find function may return map:end if RelName isn't found, and map::end shouldn't be dereferenced. 如果未找到RelName,则find函数可能返回map:end,并且不应取消引用map :: end。 You should test for that possibility and return NULL manually in that case. 您应该测试这种可能性,并在这种情况下手动返回NULL。
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