[英]Scope with Base and Derived Classes in C++
我正在努力了解我在这里遇到的问题。 这是学校课程的一项任务。 我将代码写在笔记本电脑上,然后在学校的服务器上进行编译/测试/提交。
我目前用clion编写代码。 在Mac的终端上运行gcc -v
或g++ -v
,我得到以下信息:
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 7.0.0 (clang-700.1.76)
Target: x86_64-apple-darwin15.0.0
我在学校的服务器上运行相同的命令:
gcc version 4.4.7 20120313 (Red Hat 4.4.7-16) (GCC)
我正在使用其他版本的gcc进行编译,不确定是否会影响我的问题。 向前...
int main() {
int choice; // Used to get creature selection from user
Creature *creature1, *creature2; // Objects created
printCreatureList(); // Prints list of creatures for players to select from
choice = getIntFromUser(5); // Gets user choice for creature selection
if (choice == 1) {
Goblin newGob1;
creature1 = &newGob1;
newGob1.setStats();
cout << "Created " << creature1->getName() << " as player 1's creature.\n";
// more if-else, and repeat for player 2 ...
}
现在,玩家1和玩家2各自都有一个准备战斗的生物。 请注意,稍后使用该creature1->getName()
可以正常工作。 这是战斗循环中给我一个问题的部分。 请注意,还有另一个版本,其中玩家2进行攻击,而玩家1进行防御。
do { // Enter game loop
cout << endl << "\nTurn #" << i << ", Player 1 (" << creature1->getName() << ") attacking Player 2 (" << creature2->getName() << ")";
i++;
p1Attacks(*creature1, *creature2, *p1Achilles, *p2Achilles); // Player 1 attacks, player 2 defends
if (creature2->getStrength() <= 0) { //Check if creature2 was defeated
cout << "\n\t***Player 2's creature has taken fatal damage***" << endl;
cout << "\n\t* * * Player 1 (" << creature1->getName() << ") has won the battle * * *" << endl;
winCondition = false;
break;
// advances on to p2Attacks
} while (winCondition);
我的p1Attack和p2Attack具有相似的格式:
void p1Attacks(Creature &p1, Creature &p2, bool &p1AchillesInjury, bool &p2AchillesInjury)
p1Attacks / p2Attacks正常工作,并且所有数学运算都非常完美。 但是,当我在学校服务器上运行gcc 4.4.7 20120313
我看到:
Turn #1, Player 1 () attacking Player 2 () Player 1's attack roll: 7 Player 2's defend roll: 1 Player 1's damage output: 6 Player 2's armor: 3 Player 2 damage taken: 3 Player 2 new strength: 5
第一行是不正确的,如果他们分别创建了各自的角色,则应该读Turn #1, Player 1 (The Barbarian) attacking Player 2 (Reptile)
。 在我的本地计算机上,代码可以正确运行,并按需要在括号中拼写出名称。
我的生物类以及生物.cpp中的.setStats()示例:
class Creature {
public:
Creature() {}
/*
Functions: changeStrength()
Description: Change strength attribute for creature by reducing value
Parameters: reduceStrengthBy
Preconditions: None
Postconditions: Strength is reduced
*/
void changeStrength(int reduceStrengthBy);
int getAttackDice() { return attackDice; }
int getAttackSides() { return attackSides; }
int getDefenseDice() { return defenseDice; }
int getDefenseSides() { return defenseSides; }
int getArmor() { return armor; }
int getStrength() { return strength; }
std::string getName() { return name; }
bool getDodge() { return dodge; }
protected:
int attackDice;
int attackSides;
int defenseDice;
int defenseSides;
int armor;
int strength;
std::string name;
bool dodge;
};
void Reptile::setStats() {
attackDice = 3;
attackSides = 6;
defenseDice = 1;
defenseSides = 6;
armor = 7;
strength = 18;
name = "The Reptile";
dodge = false;
}
所以我的最终问题是,为什么在早期if statement
,行creature1->getName()
在笔记本电脑和学校服务器上都能正常运行,但只能在本地计算机上使用,而稍后在远程服务器上无法使用(在p1Attack附近)?
如果一台机器上的某物有效,但另一台机器上的不适,您可以确定您已经成为不确定行为的受害者。
实际上,您正在使用悬空指针。 基本上,可以归结为:
int main(int, char**) {
int * pointer; // uninitialised, don't use
if (someCondition) {
int object = 42;
pointer = &object; // assigned to point to an object, can be used
} // object goes out of scope here
// pointer is dangling, don't use
cout << *pointer << endl; // oops
return 0;
}
为了解决这个问题,您需要将对象存储在不受自动内存管理约束的对象上(例如在堆上),或者重新排列代码以利用它。
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