CODEWITHSUNDEEP
c++stringoopreference
bmc
bmc

Reputation: 857

c++ - Pass char* through function memory deallocation error

After referencing the following resources: here and here. So I can see how the right way to do this is. Then after reading this post, I can see my previous warning was fixed through a typechar of char* "mystring" being passed into the argument of a function.

However, I am still getting the an error for a pretty intuitive couple lines of code (though I haven't touched c++ in some type, hence why I am having some trouble).

TextDocument.h

#ifndef ____TextDocument__
#define ____TextDocument__

#include <stdio.h>

class TextDocument {
    char *text;
    char *docName;
public:
    void SetText(char *otherText);
    char *GetText();
    void SetDocName(char *newName);
    char *GetDocName();
    int GetTextLength();
};

#endif /* defined(____TextDocument__) */

TextDocument.cpp

#include <iostream>
#include "TextDocument.h"
#include "string.h"
using namespace std;

void TextDocument::SetText(char *otherText){

    cout << otherText << endl;

    if (text != 0)
        delete text;          //free the memory

    text = new char[strlen(otherText)+1];   // +1 for the null char
    strcpy(text, otherText);                //text <- otherText
}

char *TextDocument::GetText(){
    return text;
}

void TextDocument::SetDocName(char *name){

    if (docName != 0)
        delete docName;

    docName = new char[strlen(name) + 1];   // +1 for the  \0 terminator
    strcpy(docName, name);                  // docName <- name
}

char *TextDocument::GetDocName(){

    return docName;
}

int TextDocument::GetTextLength(){
    if (text != 0) {
        return strlen(text);
    }
    else return 0;
}

main.cpp

#include <iostream>
#include "string.h"
#include "TextDocument.h"
#include "Folder.h"

using namespace std;

int main(void){

    TextDocument *sampleDoc;
    sampleDoc = new TextDocument;


    sampleDoc->SetText((char *)"some str"); // I have no idea why there is a linker error here.

    return 0;
}

run.sh 

g++ *.cpp -o main
./main

output:

Blakes-MacBook-Pro:data_encapsulation bmc$ sh run.sh 
some str
main(848,0x7fff7f54b300) malloc: *** error for object 0x8000000000000000: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug
run.sh: line 2:   848 Abort trap: 6           ./main

Problem 1

Why isn't it deleting my char* text when it is uncreated.

Problem 2 (Sidebar problem, not my immediate issue)

Where is the best place to put all those .h files? Example) I need #include <iostream> and using namespace std inside of a few different .h or .cpp files, where would be the best place to put them; if you put them in only the main those other modules won't be able to see it and yield errors.

1st Fix Submission

So after screwing with this thing some more, I got the error to go away with by changing the line from

if (text != 0)
    delete text;          //free the memory

to

if (text)
    delete text;          //free the memory

I guess I understand the logic if (thestringeisntempty) delete text; but why doesn't if(text != 0) delete text; work as well?

Upvotes: 0

Views: 146

Answers (1)

Phil M
Phil M

Reputation: 1619

Two solutions:

  1. Add a constructor to TextDocument that properly initializes your pointers.

    TextDocument() : text(nullptr), docName(nullptr) {}

Use NULL instead of nullptr if your compiler doesn't support the latter.

  1. Do away with char*s and use std::string.

Upvotes: 1

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