您好，我在删除我的类的成员字符串时遇到了一些麻烦，该字符串不为空并且指向正确的位置，因为我可以在之前显示我的字符串“hello world”。
之后我从另一个成员函数调用函数 mystringclass::alloc() ， this->str 应该让另一个字符串内容更大。
当我以相同的方式调整“hello”以获取“hello world”时，该过程第一次运行良好。但现在我想再次放大它并没有。所以我很困惑。
请帮我。
void mystringclass::alloc(long newsize) //newsize includes the +1 char
{
cout << "old size was: " << this->size << endl; //displays "12"
if(this->str) cout << this->str << endl; //displays "hello world" all is right till here
if(this->str) delete [] this->str ; //it crashes here
cout << "str deleted\n"; //never show up on screen
this->str = new char[newsize + 1];
this->size = newsize;
this->str[0] = 0;
}
感谢您的回答，我试图清除我的代码以将其发布在这里。我的错误消失了，但又出现了一个与三规则有关的错误：
int main()
{
stringclass str = "Hello";
stringclass str2 = str;
return 0;
}
我在整个过程中都显示信息所以问题是 str2 已经等于“你好”，甚至在我的复制构造函数中影响 str 的内容之前。并且复制后为空。怎么了？有人可能会说，我是在魔法盒中学习 c++ 的。我正在使用代码块 10.05
完整代码：
#include <fstream>
#include <iostream>
#include <vector>
using namespace std;
class stringclass
{
protected :
inline bool success() { failbit = false; return true; }
inline bool fail() { failbit = true; return false; }
public :
bool failbit;
char * mystring;
long memsize;
long length;
void alloc(long newsize);
void reset();
void copy(const stringclass & other);
stringclass() {reset(); }
stringclass(const stringclass & other) {copy(other); }
stringclass(const char str[]);
~stringclass() {delete [] mystring;}
inline long get_length() { if(mystring) length = strlen(mystring); return length;}
inline long get_memsize() const { return memsize; }
friend ostream& operator << (ostream& out, stringclass & sc){out << sc.mystring; return out;}
stringclass & operator = (stringclass & other) { copy(other); return *this;}
};
void stringclass::reset()
{
delete [] mystring;
mystring = NULL;
length = 0;
memsize = 0;
}
void stringclass::alloc(long newsize)
{
cout<< "\nalloc(long newsize)... \n" << endl;
cout << "memsize was : " << memsize << endl;
cout << "length was : " << length << endl;
if(mystring) cout << "mystring = " << mystring << endl;
delete [] mystring;
cout << "mystring deleted...\n";
mystring = new char[newsize];
cout << "mystring has been resized\n";
mystring[0] = 0;
memsize = newsize;
length = strlen(mystring);
cout << "memsize is now : " << memsize << endl;
cout << "length is now : " << length << endl;
cout<< "\nend of alloc()... " << endl;
cout << "\n";
}
void stringclass::copy(const stringclass & other)
{
cout << "\n";
cout << "copy(const stringclass & other)...\n" << endl;
cout << "other.mystring = "<< other.mystring << endl;
if(other.mystring == NULL || other.memsize == 0)
{
reset();
return;
}
alloc(other.memsize);
strcpy(mystring, other.mystring);
cout << "mystring = "<< mystring;
length = strlen(mystring);
cout << "length: " << length << endl;
cout<< "\nend of copy()... " << endl;
cout << "\n";
}
stringclass::stringclass(const char str[]) : mystring(NULL), memsize(0), length(0)
{
if(str == NULL) reset();
else
{
alloc(strlen(str) + 1);
strcpy(mystring, str);
length = strlen(mystring);
}
}
int main()
{
stringclass str = "Hello";
stringclass str2 = str;
cout << "\nback to main()...\n";
cout << "str = " << str << "\n";
cout << "str2 = " << str2 << "\n";
cout << endl;
system("PAUSE");
return 0;
}
屏幕上的结果：
alloc(long newsize)...
memsize was : 0
length was : 0
mystring deleted...
mystring has been resized
memsize is now : 6
length is now : 0
end of alloc()...
copy(const stringclass & other)...
other.mystring = Hello
alloc(long newsize)...
memsize was : 3214960
length was : 2293560
mystring = Hello
mystring deleted...
mystring has been resized
memsize is now : 6
length is now : 0
end of alloc()...
mystring = length: 0
end of copy()...
back to main()...
str =
str2 =
Appuyez sur une touche pour continuer...
我刚刚意识到您不需要以下代码：
protected :
inline bool success() { failbit = false; return true; }
inline bool fail() { failbit = true; return false; }
public :
bool failbit;
所以我推迟了这两个函数和这个变量，猜猜是什么......一切都很好，没有错误。它们甚至一次都没有使用过。我把它放回去了，问题也回来了。你怎么解释？！我已经脱发了。