C++ get process id by name

I'm trying to get a process id by name but I don't know if it's related with my pc or if I'm missing something. I've been trying for a while on changing methods but everytime I get this excpetion.

Exception thrown at 0x00007FFFC6083C0F (user32.dll) in application.exe: 0xC0000005: Access violation while reading path 0x00000000FFFFFFFF.

int getProcIdByName(string procName)
    {
        int pid = -1;

        // Open the /proc directory
        DIR* dp = opendir("/proc");
        if (dp != NULL)
        {
            // Enumerate all entries in directory until process found
            struct dirent* dirp;
            while (pid < 0 && (dirp = readdir(dp)))
            {
                // Skip non-numeric entries
                int id = atoi(dirp->d_name);
                if (id > 0)
                {
                    // Read contents of virtual /proc/{pid}/cmdline file
                    string cmdPath = string("/proc/") + dirp->d_name + "/cmdline";
                    ifstream cmdFile(cmdPath.c_str());
                    string cmdLine;
                    getline(cmdFile, cmdLine);
                    if (!cmdLine.empty())
                    {
                        // Keep first cmdline item which contains the program path
                        size_t pos = cmdLine.find('\0');
                        if (pos != string::npos)
                            cmdLine = cmdLine.substr(0, pos);
                        // Keep program name only, removing the path
                        pos = cmdLine.rfind('/');
                        if (pos != string::npos)
                            cmdLine = cmdLine.substr(pos + 1);
                        // Compare against requested process name
                        if (procName == cmdLine)
                            pid = id;
                    }
                }
            }
        }

        closedir(dp);

        return pid;
    }

    int main(int argc, char* argv[])
    {
        int pid = getProcIdByName("example.exe");
        cout << "pid: " << pid << endl;
        return 0;
    }

I also tried with this method

int findProcessID(wchar_t processName[]);

int main()
{
    // Declare a wchar_t array to put process name.
    wchar_t processName[100];

    // Input the process name, such as "notepad.exe".
    printf("Enter process name: ");
    scanf_s("%ls", processName);

    // Get the PID.
    int pid = findProcessID(processName);
    if (pid > 0) {
        printf("The process \"%ls\" is found.\n\tAnd PID is %d\n", processName, pid);
    }
    else {
        printf("Not found the process \"%ls\".\n", processName);
    }


    system("PAUSE");

    return 0;
}

int findProcessID(wchar_t processName[]) {
    // Enumerate all processes.
    PROCESSENTRY32 entry;

    // dwSize: The size of the structure, in bytes. 
    // Before calling the Process32First function, 
    // set this member to sizeof(PROCESSENTRY32). 
    // If you do not initialize dwSize, Process32First fails.
    entry.dwSize = sizeof(PROCESSENTRY32);

    // Includes all processes in the system in the snapshot.
    HANDLE snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, NULL);

    if (Process32First(snapshot, &entry) == TRUE) {
        while (Process32Next(snapshot, &entry) == TRUE) {
            if (wcscmp(entry.szExeFile, processName) == 0) {
                // Match the process name.
                return entry.th32ProcessID;
            }
        }
    }
    return -1;
}