Why can I read a dereferenced pointer, but can't write it in C, but can in C++?

I needed to patch a program, so I made a dll that I can inject and on inject it patches one byte of the instruction. The code is pretty simple, the only thing that this time I wanted to write it in C, instead of C++, just of curiosity. But when I load my dll it's thread crashes in place of writing to that pointer. The pointer is 100% and works if you do it with WriteProcessMemory, but by some reason can't be written from a dll, directly from a process. The target executable is x86 and the dll is compiled with gcc. The compilation params look like this: gcc -shared mypatch.c -o mypatch.dll

#include <Windows.h>
#include <stdio.h>
#include <TlHelp32.h>

void main()
{
    AllocConsole(); // Made a console so I can try to read the data, I thought maybe I was getting the wrong address, but I didn't.
    FILE* consoleFile;
    freopen_s(&consoleFile, "CONIN$", "r", stdin);
    freopen_s(&consoleFile, "CONOUT$", "w", stderr);
    freopen_s(&consoleFile, "CONOUT$", "w", stdout);
    DWORD relAddr = 0x123456; // My address
    DWORD addr = (DWORD)GetModuleHandle(NULL) + relAddr; // Adress is relative to the main executable.
    printf("%X", *(byte*)(addr)); // Can read the real byte
    *(byte*)(addr) = 0x90; // Can't write, crash.
    printf("%X", *(byte*)(addr)); // Can't see, crashed.
}

BOOL WINAPI DllMain(HANDLE hModule, DWORD dwReason, LPVOID lpReserved)
{
    if(dwReason == DLL_PROCESS_ATTACH)
    {
        CreateThread(0, 0, (LPTHREAD_START_ROUTINE)main, 0, 0, 0);
    }
    return 1;
}

Error message:

Unhandled exception at 0x70D41355 in SuperCoolApp.exe: 0xC0000005: Access violation writing location 0x123456. occurred