Resolving error LNK2019; unresolved external symbol

Question

I have written this code using SDL but there are some errors.

This is the code

#include <SDL.h>
#include <SDL_image.h>
#include <SDL_ttf.h>
#include <SDL_mixer.h>
#include <fstream>
#include <iostream>
using namespace std;


///////////////////////////////////    functions & global variable   ////////////////////////////////

SDL_Window* window;
SDL_Renderer* renderer;
SDL_Color textColor;
TTF_Font* font;
SDL_Surface* surface=SDL_GetWindowSurface(window);
SDL_Event event;




SDL_Texture* LoadTexture(char* path)
{
    SDL_Surface* surface = IMG_Load(path);
    SDL_Texture* texture = SDL_CreateTextureFromSurface(renderer,surface);
    SDL_FreeSurface(surface);
    return texture;
}



/////////////////////////////////////  Cell  /////////////////////////////////////

class Cell
{
private:
    char num;

public:
    Cell();
    Cell(int ,int ,char);
    char * img;
    pair <int ,int> cor;
    int flag;
    int size;
    void display();
    bool indomain(int ,int);
};


Cell :: Cell(int x ,int y ,char n){
    num=n;
    cor.first=x;
    cor.second=y;
    size=40;
    flag=0;
    if (num == '#')
        img="0.png";
    else if (num == '!')
        img="1.png";
    else
        img="street.png";
}

bool Cell :: indomain(int x ,int y){
    if ( (cor.first<=x && x<=cor.first+size) && (cor.second<=y && y<=cor.second+size))
        return true;
    return false;
}


void Cell :: display(){
    SDL_Rect rect;
    rect.x=cor.first;
    rect.y=cor.second;
    SDL_Texture* texture = LoadTexture(img);
    SDL_RenderCopy(renderer,texture,NULL,&rect);
}


////////////////////////////////////////////   Tower   /////////////////////////////////////////

class Tower
{
public:
    Tower();
    Tower(int ,int ,int ,int ,char* ,int ,int ,int);
    ~Tower();
    int price;
    int up_cost;
    char * img;
    int power;
    int domain;
    int grade;
    int index;
    pair <int ,int> cor;
    void upgrade();
    void display();
    bool mark(int ,int);
};


Tower :: Tower(int pr ,int co ,int pow ,int dom ,char* im ,int x ,int y ,int i){
    price=pr;
    up_cost=co;
    power=pow;
    domain=dom;
    img=im;
    cor.first=x;
    cor.second=y;
    grade=1;
    index=i;
}

void Tower :: upgrade(){
    if (grade<5)
    {
        grade+=1;
        power*=2;
        domain*=1.2;
        price*=1.2;
    }
}

void Tower :: display(){
    SDL_Rect rect;
    rect.x=cor.first;
    rect.y=cor.second;
    SDL_Texture* texture = LoadTexture(img);
    SDL_RenderCopy(renderer,texture,NULL,&rect);
}   

bool Tower :: mark(int x, int y){
    if ((cor.first<=x && x<=cor.first+40) && (cor.second<=y && x<=cor.second+80))
        return true;
    return false;
}





////////////////////////////////   Enemy   //////////////////////////////////////

class Enemy
{
public:
    Enemy();
    Enemy(int ,char* ,int ,int ,int);
    ~Enemy();
    char * img;
    int health;
    int cellNum;
    int index;
    pair <int ,int> cor;
    bool live();
    void display();
    void damge(Tower t);
};


Enemy :: Enemy(int h ,char* im ,int x ,int y ,int i){
    health=h;
    img=im;
    cor.first=x;
    cor.second=y;
    cellNum=0;
    index=i;
}

bool Enemy :: live(){
    if (health>0) 
        return true;
    return false;
}

void Enemy :: damge(Tower t){
    health-=t.power;
}

void Enemy :: display(){
    SDL_Rect rect;
    rect.x=cor.first;
rect.y=cor.second;
SDL_Texture* texture = LoadTexture(img);
SDL_RenderCopy(renderer,texture,NULL,&rect);
}




/////////////////////////////////////////////  Map  ///////////////////////////////////////

class Map
{
private:
char * file;
int len;

public:
Map();
Map(char* ,int);
~Map();
Cell map[15][20];
pair <int ,int> * path;
void display();
void put_tower(Tower ,Cell);
void put_enemy(Enemy ,Cell);
void remove(Cell);
void enemyMove(Enemy);
void pathFinder(int);
};


Map :: Map(char * f ,int l){
file=f;
len=l;
ifstream infile;
infile.open(file);
char * line=new char;
for (int i=0;i<15;i++)
{
    infile >> line;
    for (int j=0;j<20;j++)
        map[i][j]=Cell(j*40 ,i*40 ,line[j]);
}
this->pathFinder(len);
}

void Map :: put_enemy(Enemy e ,Cell c){
e.cor=c.cor;
e.display();
}

void Map :: put_tower(Tower t ,Cell c){
t.cor=c.cor;
t.display();
}

void Map :: remove(Cell c){
c.display();
}

void Map :: enemyMove(Enemy e){
e.cellNum+=1;
e.cor=path[e.cellNum];
}

void Map :: pathFinder(int l){
path=new pair<int ,int> [l];
ifstream infile;
infile.open(file);
char ** lines=new char* [15];
for (int i=0;i<15;i++)
    infile >> lines[i];
for (int i=0;i<20;i++)
    if (lines[0][i]=='0')
    {
        path[0]=make_pair(0,i);
        break;
    }
int x=0;
int y=path[0].second;
int ord=48;
for (int i=1;i<l;i++)
{
    if (int(lines[x-1][y])==((ord-47)%10)+48)
        x-=1;
    else if (int(lines[x+1][y])==((ord-47)%10)+48)
        x+=1;
    else if (int(lines[x][y-1])==((ord-47)%10)+48)
        y-=1;
    else if (int(lines[x][y+1])==((ord-47)%10)+48)
        y+=1;
    path[i]=make_pair(x,y);
    ord+=1;
}
}

void Map :: display(){
for (int i=0;i<15;i++)
    for (int j=0;j<20;j++)
        map[i][j].display();
}





////////////////////////////////////////////////////   Game   ////////////////////////////////////////

class Game
{
private:
int health;
int money;
int score;
int step;

public:
Game(int ,int);
~Game();
bool End;
int enemyNum;
int towerNum;
Enemy enemys[20];
Tower towers[50];
int getHealth();
int getMoney();
int getScore();
int getStep();
void setHealth(int);
void setMoney(int);
void setScore(int);
void setStep(int);
void distroy_enemy(Enemy ,Cell);
void distroy_tower(Tower ,Cell);
void shooting(Tower);
void drag_drop(Tower);
void upgradeTower(Tower);
void buyTower(Tower);
void sellTower(Tower ,Cell);
void display(Map);
void displayMenu();
void endDisplay();
bool checkEnd();
void animation();
};

Game :: Game(int h ,int m){
health=h;
money=m;
step=1;
score=0;
enemyNum=0;
towerNum=0;
End=false;
}

int Game :: getHealth(){
return health;
}
int Game :: getMoney(){
return money;
}

int Game :: getScore(){
return score;
}

int Game :: getStep(){
return step;
}

void Game :: setHealth(int h){
health=h;
}

void Game :: setMoney(int m){
money=m;
}

void Game :: setScore(int s){
score=s;
}

void Game :: setStep (int s){
step=s;
}

void Game :: distroy_enemy(Enemy e,Cell c){
for (int i=e.index;i<enemyNum-1;i++)
    enemys[i]=enemys[i+1];
enemyNum-=1;
c.display();
}

void Game :: distroy_tower(Tower t ,Cell c){
for (int i=t.index;i<towerNum-1;i++)
    towers[i]=towers[i+1];
towerNum-=1;
c.display();
}

void Game :: shooting(Tower t){
for(int i=0;i<enemyNum;i++)
{
    if (sqrt(pow(enemys[i].cor.first,2)+pow(enemys[i].cor.second,2)) <= t.domain)
        enemys[i].health-=t.power;
}
}

void Game :: upgradeTower(Tower t){
t.upgrade();
money-=t.up_cost;
}

void Game :: buyTower(Tower t){
money-=t.price;
towers[towerNum]=t;
towerNum+=1;
t.display();
}

void Game :: sellTower(Tower t ,Cell c){
distroy_tower(t,c);
money+=t.price/2;
}

void Game :: endDisplay(){
End=true;
SDL_FillRect(surface,&surface->clip_rect,SDL_MapRGB(surface->format,0XFF,0XFF,0XFF));
SDL_Surface* text;
font=TTF_OpenFont("AV.TTF",40);
textColor.b=20;
textColor.g=10;
textColor.r=0;
if (health<=0)
{
    text=TTF_RenderText_Solid(font ,"You lose" ,textColor);
}
else if (health>0)
{
    text=TTF_RenderText_Solid(font ,"Complete the mission" ,textColor);
}
SDL_Rect rect;
rect.x=300;
rect.y=300;
SDL_BlitSurface(text,NULL,surface,&rect);
}

bool Game :: checkEnd(){
if (health<=0 || step==20)
    return true;
return false;
}    

void Game :: displayMenu(){
SDL_Rect rect;
rect.x=800;
rect.y=0;
SDL_Texture* texture = LoadTexture("menu.png");
SDL_RenderCopy(renderer,texture,NULL,&rect);
}


void Game :: display(Map m){
m.display();
for (int i=0;i<towerNum;i++)
    towers[i].display();
for (int i=0;i<enemyNum;i++)
    enemys[i].display();
this->displayMenu();
/////////// ttf
}

void Game :: animation(){
SDL_Rect Lrect;
Lrect.x=83;
Lrect.y=0;
SDL_Rect Rrect;
Rrect.x=915;
Rrect.y=0;
SDL_Texture* leftpic = LoadTexture("left.png");
SDL_Texture* rightpic = LoadTexture("right.png");
for (int i=0;i<12;i++)
{
    SDL_RenderCopy(renderer,leftpic,NULL,&Lrect);
    SDL_RenderCopy(renderer,rightpic,NULL,&Rrect);
    Rrect.x-=20;
    Lrect.x+=60;
    SDL_RendererFlip();
    SDL_Delay(300);
}
}





//////////////////////////////////////////////////////////////    main    //////////////////////////////////////////////////////////////////////


int main()
{
window=SDL_CreateWindow("Frontline Defence",SDL_WINDOWPOS_UNDEFINED,
    SDL_WINDOWPOS_UNDEFINED,940,600,SDL_WINDOW_SHOWN);
Game game(1000,500);
Map map("map.txt",30);
while ( !game.checkEnd() )
    {
        if ( SDL_PollEvent(&event))
        {
            if (event.type == SDL_QUIT)
                return 0;
            if (event.type == SDL_MOUSEBUTTONDOWN )
            {
                SDL_Delay(3000);
            }
        }
    }
    game.endDisplay();
    return 0;
}

I've done every thing I could but nothing changed! I've tried including the libraries , typing all parts of the code in the main file and many other ways but it didn't help

These are the errors:

Error   12  error LNK1120: 8 unresolved externals   C:\Users\FUJITSU\Desktop\frontline defence\project\ConsoleApplication1\Debug\ConsoleApplication1.exe    ConsoleApplication1
Error   4   error LNK2019: unresolved external symbol "public: __thiscall Cell::Cell(void)" (??0Cell@@QAE@XZ) referenced in function "public: __thiscall Map::Map(char *,int)" (??0Map@@QAE@PADH@Z) C:\Users\FUJITSU\Desktop\frontline defence\project\ConsoleApplication1\ConsoleApplication1\classes.obj  ConsoleApplication1
Error   8   error LNK2019: unresolved external symbol "public: __thiscall Enemy::~Enemy(void)" (??1Enemy@@QAE@XZ) referenced in function "public: __thiscall Game::Game(int,int)" (??0Game@@QAE@HH@Z)   C:\Users\FUJITSU\Desktop\frontline defence\project\ConsoleApplication1\ConsoleApplication1\classes.obj  ConsoleApplication1
Error   7   error LNK2019: unresolved external symbol "public: __thiscall Enemy::Enemy(void)" (??0Enemy@@QAE@XZ) referenced in function "public: __thiscall Game::Game(int,int)" (??0Game@@QAE@HH@Z)    C:\Users\FUJITSU\Desktop\frontline defence\project\ConsoleApplication1\ConsoleApplication1\classes.obj  ConsoleApplication1
Error   10  error LNK2019: unresolved external symbol "public: __thiscall Game::~Game(void)" (??1Game@@QAE@XZ) referenced in function "int __cdecl SDL_main(void)" (?SDL_main@@YAHXZ)   C:\Users\FUJITSU\Desktop\frontline defence\project\ConsoleApplication1\ConsoleApplication1\classes.obj  ConsoleApplication1
Error   9   error LNK2019: unresolved external symbol "public: __thiscall Map::~Map(void)" (??1Map@@QAE@XZ) referenced in function "int __cdecl SDL_main(void)" (?SDL_main@@YAHXZ)  C:\Users\FUJITSU\Desktop\frontline defence\project\ConsoleApplication1\ConsoleApplication1\classes.obj  ConsoleApplication1
Error   6   error LNK2019: unresolved external symbol "public: __thiscall Tower::~Tower(void)" (??1Tower@@QAE@XZ) referenced in function "public: __thiscall Game::Game(int,int)" (??0Game@@QAE@HH@Z)   C:\Users\FUJITSU\Desktop\frontline defence\project\ConsoleApplication1\ConsoleApplication1\classes.obj  ConsoleApplication1
Error   5   error LNK2019: unresolved external symbol "public: __thiscall Tower::Tower(void)" (??0Tower@@QAE@XZ) referenced in function "public: __thiscall Game::Game(int,int)" (??0Game@@QAE@HH@Z)    C:\Users\FUJITSU\Desktop\frontline defence\project\ConsoleApplication1\ConsoleApplication1\classes.obj  ConsoleApplication1
Error   11  error LNK2019: unresolved external symbol _SDL_main referenced in function _main    C:\Users\FUJITSU\Desktop\frontline defence\project\ConsoleApplication1\ConsoleApplication1\SDL2main.lib(SDL_windows_main.obj)   ConsoleApplication1

Answer 1

You're getting the linker errors referencing constructors and destructors because you haven't provided any implementation for those functions (as Michael Burr pointed out in a comment).

The unresolved external symbol _SDL_main referenced in function _main is because the mainfunction needs to have a specific signature: int main(int argc, char* argv[]) and check that you also have the SDL2main.libin the input to the linker.

Finally, it would seem that you never create any renderer (unless you create somewhere not included in your code example), so you have to add a call to SDL_CreateRenderer() after you create the SDL_Window in main.