1
我正在通過Accelerated C++的方式工作，並決定解決那裏定義的結構之一。雖然這樣做，但我遇到了一個問題：創建這些結構的向量並修改每個結構中的元素似乎都會修改其中的所有元素。我知道這可能意味着我已經將向量中的所有結構初始化爲單個內存地址處的結構，但我使用.push_back（）方法將「虛擬」結構插入到向量中。我的印象是.push_back（）推入了它的參數副本，有效地創建了一個新的結構體。C++：爲什麼我的向量結構作爲一個結構？
下面是結構的標題：
#ifndef _STUDENT_INFO__CHAPTER_9_H
#define _STUDENT_INFO__CHAPTER_9_H
#include <string>
#include <iostream>
#include <vector>
class Student_info9{
public:
Student_info9(){homework = new std::vector<double>;};
Student_info9(std::istream& is);
std::string getName() const {return name;};
double getMidterm() const {return midterm;};
double getFinal() const {return final;};
char getPassFail() const {return passFail;};
std::vector<double> *getHw(){return homework;};
void setName(std::string n) {name = n;};
void setMidterm(double m) {midterm = m;};
void setFinal(double f) {final = f;};
private:
std::string name;
double midterm;
double final;
char passFail;
std::vector<double> *homework;
};
#endif /* _STUDENT_INFO__CHAPTER_9_H */
這裏是我與（原諒過度print語句打打鬧鬧的代碼......一段時間嘗試調試結果:) ）：
vector<Student_info9> did9, didnt9;
bool did_all_hw9(Student_info9& s)
{
vector<double>::const_iterator beginCpy = s.getHw()->begin();
vector<double>::const_iterator endCpy = s.getHw()->end();
return(find(beginCpy, endCpy, 0) == s.getHw()->end());
}
void fill_did_and_didnt9(vector<Student_info9> allRecords)
{
vector<Student_info9>::iterator firstDidnt = partition(allRecords.begin(), allRecords.end(), did_all_hw9);
vector<Student_info9> didcpy(allRecords.begin(), firstDidnt);
did9 = didcpy;
vector<Student_info9> didntcpy(firstDidnt, allRecords.end());
didnt9 = didntcpy;
}
int main(int argc, char** argv) {
vector<Student_info9> students;
Student_info9 record;
for(int i = 0; i < 5; i++)
{
students.push_back(record);
}
for(int i = 0; i < students.size(); i++)
{
students[i].setMidterm(85);
students[i].setFinal(90);
students[i].getHw()->push_back(90);
std::cout << "student[" << i << "]'s homework vector size is " << students[i].getHw()->size() << std::endl;
students[i].getHw()->push_back(80);
std::cout << "student[" << i << "]'s homework vector size is " << students[i].getHw()->size() << std::endl;
students[i].getHw()->push_back(70);
std::cout << "student[" << i << "]'s homework vector size is " << students[i].getHw()->size() << std::endl;
std::cout << "Just pushed back students[" << i << "]'s homework grades" << std::endl;
if(i == 3)
students[i].getHw()->push_back(0);
}
std::cout << "student[3]'s homework vector size is " << students[3].getHw()->size() << std::endl;
for(vector<double>::const_iterator it = students[3].getHw()->begin(); it != students[3].getHw()->end(); it++)
std::cout << *it << " ";
std::cout << std::endl;
std::cout << "students[3] has " << ((find(students[3].getHw()->begin(),students[3].getHw()->end(), 0) != students[3].getHw()->end()) ? "atleast one " : "no ")
<< "homework with a grade of 0" << std::endl;
fill_did_and_didnt9(students);
std::cout << "did9's size is: " << did9.size() << std::endl;
std::cout << "didnt9's size is: " << didnt9.size() << std::endl;
}
正如你可以打印報表看，似乎功課成績被添加到只有一個Student_info9對象，其副本似乎填充整個矢量。我的印象是，如果您要在單個對象上使用連續的.push_back（）副本，則會創建該對象的副本，每個副本具有不同的內存地址。
我不確定這是否是問題的根源，但希望有人能指出我正確的方向。
謝謝。
順便說一下，這些標頭警衛[非法]（http：// stackoverflow。COM /問題/ 228783 /什麼，是最規則有關，使用安下劃線-IN-A-C-標識符）。 – GManNickG 2011-01-20 17:48:47