this code works

gistfile1.cpp

// GDAL_WARPTEST.cpp : Defines the entry point for the console application.
#include "stdafx.h"
#include "gdal_priv.h"   
#include <iostream>
using namespace std;
//#include "cpl_conv.h" // for CPLMalloc()
//#include <stdio.h>

int _tmain(int argc, _TCHAR* argv[])
{
	GDALDataset* raster;     // declare the GDALDataset we will create
  	GDALAllRegister();  // Attempts to register all known drivers, required to recognize bmp file
    const char* filenameImg = "img/cea.tif";    // identifies the file we want to open
    raster = (GDALDataset*) GDALOpen(filenameImg, GA_ReadOnly); // opens file
    if (raster == NULL) 
    {
        cout << "Something went wrong!\n";
    }
    else cout << "Image opened successfully!\n";

    int rasterXSize = raster->GetRasterXSize();
    int rasterYSize = raster->GetRasterYSize() ;
    cout << "x size is " << rasterXSize << "\n";
    cout << "y size is " << rasterYSize << "\n";
       
    int pixelX = rasterXSize + 1;
    while (pixelX > rasterXSize || pixelX < 0) {
        cout << "Enter pixel X coordinate: ";
        scanf("%d", &pixelX);
        getc(stdin);
        if (pixelX > rasterXSize) cout << "X coordinate must be less than X size of image\n";
    }
    cout << "Pixel X = " << pixelX << "\n";

    int pixelY = rasterYSize + 1;
    while (pixelY > rasterYSize || pixelY < 0) {
        cout << "Enter pixel Y coordinate: ";
        scanf("%d", &pixelY);
        getc(stdin);
        if (pixelY > rasterYSize) cout << "Y coordinate must be less than Y size of image\n";
    }
    cout << "Pixel Y = " << pixelY << "\n";

    float lati;
    float longi;
    cout << "Latitude: ";
    scanf("%f", &lati);
    getc(stdin);
    cout << "Latitude = " << lati << "\n";
    cout << "Longitude: ";
    scanf("%f", &longi);
    getc(stdin);
    cout << "Longitude = " << longi << "\n";

    // create a GCP
    GDAL_GCP firstGCP;
    firstGCP.pszId = "1";
    firstGCP.pszInfo = "";
    firstGCP.dfGCPPixel = pixelX;
    firstGCP.dfGCPLine = pixelY;
    firstGCP.dfGCPX = lati;
    firstGCP.dfGCPY = longi;
    firstGCP.dfGCPZ = 0;

    // Driver tests
    const char* outputFilename = "img/output.tif";   
    GDALDriver* driverName = GetGDALDriverManager()-> GetDriverByName("GTiff");

    GDALDataset* outputRaster = driverName->CreateCopy(outputFilename, raster, FALSE,
                                           NULL, NULL, NULL);

    if (outputRaster != NULL) GDALClose( (GDALDatasetH) outputRaster);
    if (raster != NULL) GDALClose( (GDALDatasetH) raster);

    getc(stdin);
    return 0;
}

correct syntax is GDALDataset->methodName();