Cannot compile example code

[sylvain]

Hi, this is an example code from Stroustrup. G++ compiler made me add 7 declarations. Even with these additions compiler does not finish. Now compiler says to me : collect2 ; error : ld returned 1 exit status.
I understand nothung from the above. I hope somebody will help me. Many thanks.
Here is the code :
/*string.cpp*/
#include<iostream>
using namespace std;
class String {
struct Srep; // representation
Srep *rep;
class Cref; // reference to char
public:
class Range { }; // for exceptions
String(); // x = ""
String(const char*); // x = "abc"
String(const String&); // x = other_string
String& operator=(const char *);
String& operator=(const String&);
~String();
void check(int i) const;
char read(int i) const;
void write(int i, char c);
Cref operator[](int i);
char operator[](int i) const;
int size() const;
String& operator+=(const String&);
String& operator+=(const char*);
friend ostream& operator<<(ostream&, const String&);
friend istream& operator>>(istream&, String&);
friend bool operator==(const String& x, const char* s);
friend bool operator==(const String& x, const String& y);
friend bool operator!=(const String& x, const char* s);
friend bool operator!=(const String& x, const String& y);
};
String operator+(const String&, const String&);
String operator+(const String&, const char*);
struct String::Srep {
char* s; // pointer to elements
int sz; // number of characters
int n; // reference count
string strcpy(string, string); // declaration I added
Srep(int nsz, const char* p)
{
n = 1;
sz = nsz;
s = new char[sz+1]; // add sace for terminator
strcpy(s,p);
}
~Srep() { delete[] s; }
Srep* get_own_copy() // clone if necessary
{
if (n==1) return this;
n--;
return new Srep(sz,s);
}
void assign(int nsz, const char* p)
{
if (sz != nsz) {
delete[] s;
sz = nsz;
s = new char[sz+1];
}
strcpy(s,p);
}
private: // prevent copying:
Srep(const Srep&);
Srep& operator=(const Srep&);
};
class String::Cref { // reference to s[i]
friend class String;
String& s;
int i;
Cref(String& ss, int ii) : s(ss), i(ii) { }
Cref(const Cref& r) : s(r.s), i(r.i) { }
Cref(); // not defined, never used
public:
operator char() const { s.check(i); return s.read(i); } // yield value
void operator=(char c) { s.write(i,c); } // change value
};
String::String() // the empty string is the default value
{
rep = new Srep(0,"");
}
String::String(const String& x) // copy constructor
{
x.rep->n++;
rep = x.rep; // share representation
}
String::~String()
{
if (--rep->n == 0) delete rep;
}
String& String::operator=(const String& x) // copy assignment
{
x.rep->n++; // protects against ``st = st''
if (--rep->n == 0) delete rep;
rep = x.rep; // share representation
return *this;
}
String::String(const char* s)
{
int strlen(char const*); // declaration I added
rep = new Srep(strlen(s),s);
}
String& String::operator=(const char* s)
{
int strlen(char const*); // declaration I added
if (rep->n == 1) // recycle Srep
rep->assign(strlen(s),s);
else { // use new Srep
rep->n--;
rep = new Srep(strlen(s),s);
}
return *this;
}
void String::check(int i) const
{
if (i<0 || rep->sz<=i) throw Range();
}
char String::read(int i) const
{
return rep->s[i];
}
void String::write(int i, char c)
{
rep=rep->get_own_copy();
rep->s[i]=c;
}
String::Cref String::operator[](int i)
{
check(i);
return Cref(*this,i);
}
char String::operator[](int i) const
{
check(i);
return rep->s[i];
}
int String::size() const
{
return rep->sz;
}
ostream& operator<<(ostream& os, const String& s)
{
return os << s.rep->s;
}
#include<string>
istream& operator>>(istream& is, String& s)
// this implementation is "almost cheating" :-)
{
string ss;
is >> ss;
s = ss.c_str();
return is;
}
bool operator==(const String& x, const char* s)
{
bool strcmp(string f, string g); // declaration I added
return strcmp(x.rep->s, s) == 0;
}
bool operator==(const String& x, const String& y)
{
bool strcmp(string f, string g); // declaration i added
return strcmp(x.rep->s, y.rep->s) == 0;
}
bool operator!=(const String& x, const char* s)
{
bool strcmp(string, string); // declaration i added
return strcmp(x.rep->s, s) != 0;
}
bool operator!=(const String& x, const String& y)
{
bool strcmp(string, string); // declaration I added
return strcmp(x.rep->s, y.rep->s) != 0;
}
void ff(String s, const String& r)
{
char c1 = s[1]; // c1 = s.operator[](1).operator char()
s[1] = 'c'; // s.operator[](1).operator=('c')
char c2 = r[1]; // c2 = r.operator[](1)
// r[1] = 'd'; // error: assignment to non-lvalue char, r.operator[](1) = 'd'
}
int hash(const String& s)
{
int h = s.read(0);
const int max = s.size();
for (int i = 1; i<max; i++) h ^= s.read(i)>>1; // unchecked access to s
return h;
}
String f(String a, String b)
{
a[2] = 'x';
char c = b[3];
cout << "in f: " << a << ' ' << b << ' ' << c << '\n';
return b;
}
int main()
// very simple minded first test
{
String x, y;
cout << "Please enter two strings\n";
cin >> x >> y;
cout << "input: " << x << ' ' << y << '\n';
String z = x;
y = f(x,y);
if (x != z) cout << "x corrupted!\n";
x[0] = '!';
if (x == z) cout << "write failed!\n";
cout << "exit: " << x << ' ' << y << ' ' << z << '\n';
}



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[PacR]

Disch wrote:

Put your code in code tags

[code]paste your code here

[/code]

[Chervil]

1. Remove the lines tagged with

    // declaration I added 

or simply go back to the original code.

2. Then, at the start, add the required header include statement,

#include <cstring> 

see http://www.cplusplus.com/reference/cstring/

[sylvain]

To Chervil. Many thanks. I removed my 7 declarations and added <string> header. Compiler g++ asks me again to put declarations. I hope you'll help me again. Sylvain

[Chervil]

I removed my 7 declarations and added <string> header.

Note the header which is needed for strcpy, strlen, strcmp is <cstring>, not <string>

[sylvain]

Ouf! Compiler says OK. Thank you very much for your help.