First-chance exception in ConsoleApplication2.exe: 0xC0000005: Access violation writing, c++

Question

I'm playing with some code and trying to make it work but seems that I'm missing something... so can anyone please tell me what did I miss or do wrong? program breaks at *(sData->pFileBuffer+i) ^=*(sData->pKey+j);

Here is the full code: I'm compiling in visual studio 2012 if that has something to do with it...

#include <iostream>
using namespace std;

/*
struct StubData{
char * pFileBuffer;
long long FileSize;
char * pKey;
long KeySize;
};*/


class StubData{
public:
    char *pFileBuffer;
    long long FileSize;
    char *pKey;
    long KeySize;
    StubData(){}
 };





void Decrypt(StubData * sData){
    int i=0,j=0; 


for(i;i<sData->FileSize;i++){
    *(sData->pFileBuffer+i) ^=*(sData->pKey+j);
    j++;
    if (j>=sData->KeySize)j=0;
}

}


void Encrypt(StubData * sData){
    int i,j;

    sData->pKey="mysecretpassword";
    sData->KeySize=strlen(sData->pKey);

    j=0;

    printf("[*]Encoding\n");  
    for(i=0;i<sData->FileSize;i++)
    {
        *(sData->pFileBuffer+i) ^=*(sData->pKey+j);
        j++;
        if (j>=sData->KeySize)j=0;
    }
}


void main(){
    //StubData S;
    StubData *S = (StubData *)malloc(sizeof(StubData));
    new (S) StubData;

    S->pFileBuffer="MARKO";
    S->FileSize=strlen(S->pFileBuffer);

    Encrypt(S);
    cout<<"\nenc\n"<<S->pFileBuffer;

    Decrypt(S);
    cout<<"\ndec\n"<<S->pFileBuffer;
}

Answer 1

You assign a charater string literal to S->pFileBuffer

S->pFileBuffer="MARKO";

These character strings literals are immutable (often compiled into .rodata). If you want a mutable character string you should allocate it somewhere.

You can do something like

char str[] = "MARKO";  //be careful, if this goes out of scope before S, then S has a dangling pointer
S->pFileBuffer=str;

This is not very C++-like. But the rest of your code doesn't seem very C++-like either.