作为 Accelerated C++ 问题 12.1 的一部分，我正在实现一个字符串类。主要是这个构造函数：
Str(const char* cp) {
std::copy(cp, cp+std::strlen(cp), std::back_inserter(*this));
}
这似乎在back_inserter调用时引起了问题push_back：
void Str::push_back( const char& c){
if ((data + length) == limit){
grow();
}
unchecked_append(c);
}
这似乎在调用grow()但在执行任何grow().
void Str::grow()
{
// when growing, allocate twice as much space as currently in use
size_type new_size = std::max(2 * (limit - data), ptrdiff_t(1));
// allocate new space and copy existing elements to the new space
iterator new_data = alloc.allocate(new_size);
iterator new_avail = std::uninitialized_copy(data, (data+length), new_data);
// return the old space
uncreate();
// reset pointers to point to the newly allocated space
data = new_data;
limit = data + new_size;
}
具体来说，它会导致 Windows 说“Str.exe 已停止工作”，并导致 Ubuntu 仅报告分段错误。
这是我的完整代码：
#ifndef _GUARD_STR_H
#define _GUARD_STR_H
#include <ctype.h>
#include <memory>
#include <iterator>
#include <iostream>
#include <cstddef>
#include <cstring>
class Str {
friend std::istream& operator>>(std::istream&, Str&);
public:
typedef size_t size_type;
typedef char * iterator;
typedef const char * const_iterator;
typedef char& reference;
typedef const char& const_reference;
typedef char value_type;
Str& operator+=(const Str& s){
std::copy(s.begin(), s.end(),
std::back_inserter(*this));
return *this;
}
// default constructor; create an empty Str
Str() { create();}
// create a Str containing n copies of c
Str(size_type n, char c){ }
iterator end() { return data + length; }
iterator begin() { return data; }
const_iterator end() const { return data + length; }
const_iterator begin() const { return data; }
// create a Str from a null-terminated array of char
Str(const char* cp) {
std::copy(cp, cp+std::strlen(cp), std::back_inserter(*this));
}
template<class In> Str(In i, In j) {
std::copy(i, j, std::back_inserter(data));
}
std::allocator<char> alloc;
void push_back( const char&);
char& operator[](size_type i) { return data[i]; }
const char& operator[](size_type i) const { return data[i]; }
size_type size() const { return length; }
private:
iterator data;
size_t length;
iterator limit;
void create();
void create(size_type, char);
void grow();
void unchecked_append(const char& c);
void uncreate();
};
void Str::push_back( const char& c){
if ((data + length) == limit){
grow();
}
unchecked_append(c);
}
void Str::unchecked_append(const char & val)
{
alloc.construct((data+(length++)), val);
}
void Str::uncreate()
{
if (data) {
// destroy (in reverse order) the elements that were constructed
iterator it = (data + length);
while (it != data)
alloc.destroy(--it);
// return all the space that was allocated
alloc.deallocate(data, limit - data);
}
// reset pointers to indicate that the Vec is empty again
data = limit = 0;
}
void Str::create(){
data = limit = 0;
}
void Str::create(size_type n, char c){
data = alloc.allocate(n);
std::uninitialized_fill(data, data + n, c);
}
void Str::grow()
{
// when growing, allocate twice as much space as currently in use
size_type new_size = std::max(2 * (limit - data), ptrdiff_t(1));
// allocate new space and copy existing elements to the new space
iterator new_data = alloc.allocate(new_size);
iterator new_avail = std::uninitialized_copy(data, (data+length), new_data);
// return the old space
uncreate();
// reset pointers to point to the newly allocated space
data = new_data;
limit = data + new_size;
}
std::ostream& operator<<(std::ostream&, const Str&);
Str operator+(const Str&, const Str&);
std::ostream& operator<<(std::ostream& os, const Str& s)
{
for (Str::size_type i = 0; i != s.size(); ++i)
os << s[i];
return os;
}
std::istream& operator>>(std::istream& is, Str& s)
{
char c;
while (is.get(c)){
s.push_back(c);
}
return is;
}
Str operator+(const Str& s, const Str& t)
{
Str r = s;
r += t;
return r;
}
#endif
是什么导致了分段错误？