Invalid File Handle error in my program

Hello everyone,
I am having trouble figuring out where the bug is in my code.
I have two functions which are used to access a serial port.
When i combine then it works correctly ,but when i split them into smaller functions i get "INVALID_FILE_HANDLE"(getlasterror code number : 6)
IN serial_functions

Code:

---

#include <serial_functions.h>
void serialport_init(HANDLE hSerial)
{
    hSerial = CreateFile("COM3",GENERIC_READ | GENERIC_WRITE,0,0,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,0);
    if(hSerial==INVALID_HANDLE_VALUE)
    {
        if(GetLastError()==ERROR_FILE_NOT_FOUND)
        {
            printf("Serial Port does not exist.\n");
            exit(1);
        }
        printf("Some other error occured.\n");
        exit(1);
    }
    //printf("%d\n",GetHandleInformation(hSerial, lpdwFlags));
    //getch();
    printf("Port opened succesfully.\n");


    if (!GetCommState(hSerial, &dcbSerialParams))
    {
        printf("Error getting state.\n");
        exit(2);
    }
    dcbSerialParams.BaudRate=CBR_19200;
    dcbSerialParams.ByteSize=8;
    dcbSerialParams.StopBits=ONESTOPBIT;
    dcbSerialParams.Parity=NOPARITY;
    if(!SetCommState(hSerial, &dcbSerialParams))
    {
        printf("Error setting serial port state.\n");
    }
    printf("Parameters set.\n");
    timeouts.ReadIntervalTimeout=50;
    timeouts.ReadTotalTimeoutConstant=50;
    timeouts.ReadTotalTimeoutMultiplier=10;
    timeouts.WriteTotalTimeoutConstant=50;
    timeouts.WriteTotalTimeoutMultiplier=10;
    if(!SetCommTimeouts(hSerial, &timeouts))
    {
        printf("Error setting timeouts.\n");
        exit(3);
    }
    printf("Timeouts set.\n");
}
void writedata(HANDLE hSerial,char *b,int n)
{
    if(!WriteFile(hSerial, *b, n, &dwBytesRead, NULL))
    {
        printf("Error occured while writting data.\n");
        //printf("%d\n",GetHandleInformation(hSerial, lpdwFlags));
        //system("pause");
        exit(5);
    }
    printf("Data Sent.\n");
}
/*
void readdata(int n)
{
    if(!ReadFile(hSerial, rzBuff, n, &dwBytesRead, NULL))
    {
        printf("Error occured while reading data.\n");
        exit(4);
    }
}
*/

---

And in my main.c

Code:

---

#include "main.h"
#include "serial_functions.h"
int main()
{
    printf("\n");
    serialport_init(hSerial);
    pointer_xyz = xyz;
    writedata(hSerial,pointer_xyz,1);


    return 0;
}

---

The program compiles and runs fine but i am not able to get the desired result in "writedata(hSerial,pointer_xyz,1);"

When i merge the two functions they work perfectly :(
Any help would be appreciated.

To change a parameter passed to a function inside a function there is two ways.
1. One return the changed parameter using the return keyword.
2. Pass the parameter via pointer (and in C++ you can also use via reference)

I suggest re-reading the section of the book on pointers; or if pointers have not yet been discussed in the book using the "return" keyword.

Tim S.

Hello Tim,
Thank you for you reply.

There did make a mistake in my earlier post.
I am passing just b not *b in my function.I realized i had made that mistake after reading your post.
Anyway i got the result using return.

Code:

---

#include "serial_functions.h"
int main()
{
    printf("\n");
    myhandle = serialport_init(hSerial);  //myhandle is a handle
    pointer_xyz = xyz;
    writedata(myhandle,pointer_xyz,1);
    return 0;
}

---

In serial_functions.c

Code:

---

#include "serial_functions.h"
HANDLE serialport_init(HANDLE hSerial)
{
    hSerial = CreateFile("COM5",GENERIC_READ | GENERIC_WRITE,0,0,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,0);
    if(hSerial==INVALID_HANDLE_VALUE)
    {
        if(GetLastError()==ERROR_FILE_NOT_FOUND)
        {
            printf("Serial Port does not exist.\n");
            exit(1);
        }
        printf("Some other error occurred.\n");
        exit(1);
    }
    printf("Port opened successfully.\n");


    if (!GetCommState(hSerial, &dcbSerialParams))
    {
        printf("Error getting state.\n");
        exit(2);
    }
    dcbSerialParams.BaudRate=CBR_19200;
    dcbSerialParams.ByteSize=8;
    dcbSerialParams.StopBits=ONESTOPBIT;
    dcbSerialParams.Parity=NOPARITY;
    if(!SetCommState(hSerial, &dcbSerialParams))
    {
        printf("Error setting serial port state.\n");
    }
    printf("Parameters set.\n");
    timeouts.ReadIntervalTimeout=50;
    timeouts.ReadTotalTimeoutConstant=50;
    timeouts.ReadTotalTimeoutMultiplier=10;
    timeouts.WriteTotalTimeoutConstant=50;
    timeouts.WriteTotalTimeoutMultiplier=10;
    if(!SetCommTimeouts(hSerial, &timeouts))
    {
        printf("Error setting timeouts.\n");
        exit(3);
    }
    printf("Timeouts set.\n");
    return hSerial;
}
void writedata(HANDLE hSerial,char *b,int n)
{
    if(!WriteFile(hSerial, b, n, &dwBytesRead, NULL))
    {
        printf("Error occurred while writing data.\n");
        exit(5);
    }
    printf("Data Sent.\n");
}

---

Could you please tell me how to do it via pointers.