C++ - '(const char*)' not declared in scope? [closed] - c++

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I want to make a custom String class for C++. But when I do this:
g++ test.cpp sys/Base.h sys/Base.cpp
I get this error:
sys/Base.cpp: In function 'const char* Base::toChar()':
sys/Base.cpp:57:13: error: 'strval' was not declared in this scope
return strval;
^
sys/Base.cpp: In function 'std::string Base::toStr()':
sys/Base.cpp:60:20: error: 'strval' was not declared in this scope
return string(strval);
^
test.cpp
#include "sys/Base.h"
int main() {
Base::write("Hello there.\n");
return 0;
}
sys/Base.h
// Header file handling
#ifndef ARAVK_BASE_H
#define ARAVK_BASE_H
// Includes
#include <string>
// Global variables
#define EXIT_YAY 0
#define EXIT_ERR 1
using namespace std;
namespace Base {
// Classes:
class String {
static const char* strval;
public:
// Constructors:
String();
String(char[]);
String(const char*);
String(string);
// Destructors:
~String();
// Operators:
// =
void operator=(const String&);
void operator=(const char*&);
void operator=(const string&);
// Conversion:
const char* toChar() const;
string toStr() const;
};
// Functions:
// Input-Output:
// Write:
void write(String);
void write(string);
void write(const char*);
// Read:
String read();
// Executing:
String run(String);
}
#endif
sys/Base.cpp
// Including
#include "Base.h"
#include <string>
#include <stdio.h>
#include <stdlib.h>
#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
// Global variables
#define EXIT_ERR 1
#define EXIT_YAY 0
/* ------------------------ */
using namespace std;
namespace Base {
// Classes
// String functions
// Constructors
String::String() {
const char* strval = "";
}
String::String(const char* str) {
const char* strval = str;
}
String::String(string str) {
const char* strval = str.c_str();
}
String::String(char str[]) {
const char* strval = str;
}
// Destructors
String::~String() {
delete strval;
}
// Operators
// =
void String::operator=(const String &strp) {
strval = strp.toChar();
}
void String::operator=(const char* &strp) {
strval = strp;
}
void String::operator=(const string &strp) {
strval = strp.c_str();
}
// Conversion:
const char* toChar() {
return strval;
}
string toStr() {
return string(strval);
}
// Functions:
// Input-Output:
// Write
void write(String str) { printf(str.toChar()); }
void write(const char* str) { printf(str); }
void write(string str) { printf(str.c_str()); }
// Read
String read() { char str[100]; scanf("%s", str); return String(str); }
//TODO: More to come
// Executing
/*String run(String command) {
const char* cmd = command.toChar();
char buffer[128];
string result = "";
std::shared_ptr<FILE> pipe(popen(cmd, "r"), pclose);
if (!pipe) throw runtime_error("popen() failed!");
while (!feof(pipe.get())) {
if (fgets(buffer, 128, pipe.get()) != NULL)
result += buffer;
}
return String(result);
}*/
String run(String command) {
char buffer[128];
std::string result = "";
const char* cmd = command.toChar();
FILE* pipe = popen(cmd, "r");
if (!pipe) throw std::runtime_error("popen() failed!");
try {
while (!feof(pipe)) {
if (fgets(buffer, 128, pipe) != NULL)
result += buffer;
}
} catch (...) {
pclose(pipe);
throw;
}
pclose(pipe);
return String(result);
}
}
I'm not sure why this is happening. I think it's related to how I've declared/defined the const char* 'strval'. Can anybody help?
P.S: If the answer is too big, this project is on Github: AravK/C-Applications

Answer 1

Let's take a look at your constructor:
String::String() {
const char* strval = "";
}
This declares a local variable called strval. The variable is local to the constructor; it doesn't exist once execution of the constructor completes.
What you need instead is a member variable - declare it inside the class, but not inside a member method or constructor. In fact, you have already defined it as such in the header file:
class String {
static const char* strval;
So, remove the const char * from your constructor and add a class qualifier, so that the line becomes an assignment to the existing variable, rather than creation of a local:
String::String() {
String::strval = "";
}
And also change the return statement that is giving you the error:
return String::strval;
Or perhaps - and this is likely what you really wanted - remove the static qualifier from the variable definition, and change the constructor instead to just:
String::String() {
strval = "";
}
Furthermore, your destructor incorrectly deletes data that was not necessarily dynamically allocated, or which may belong to another object:
String::~String() {
delete strval;
}
This requires re-working. At the moment the simplest solution is to remove the delete strval altogether.
Your read() function potentially instigates a buffer overflow, by using scanf("%s") with a fixed size buffer and unknown input size:
char str[100]; scanf("%s", str); return String(str);
Finally, your command line:
g++ test.cpp sys/Base.h sys/Base.cpp
... should not include the header file (Base.h). You are specifying the units you want compiled, and Base.h is already included in Base.cpp; it is not a standalone unit that should be compiled invidually.

Answer 2

yes you did not define the variable in your class as a field.
there is 3 locals déclaration in your constructors.
just add it the way you have done in the header.
static const char* strval
and remove the définition in your constructors. Just keep the assignement part.
regards