SegFault Error, Need Help

The program below is supposed to first, open the port, then send a command and wait for the port to say it is done. Then after all the commands are sent, it closes the port and ends the program. After sending four commands to the port, the program errors out and says it is a segfault error. If anyone can figure out what is going on, please let me know.

Code:

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#include <stdio.h>
#include <windows.h>
#include <stdlib.h>
#include <conio.h>

int configure(void);  // function prototype
int run(void); // function prototype
int a; // initializing of variable a
int b; // initializing of variable b



int main()
{
    printf("Running Program.\n");
    typedef long(*importFunction1)(long, long); //OpenPort signature
    typedef long(*importFunction2)(char*); //DriverSendToPort signature
    typedef long(*importFunction3)(char*, long); //WaitForChar signature
    typedef long(*importFunction4)(void); //ClosePort signature
   
        //Loading all functions at one time.
    importFunction1 OpenPort;
    importFunction2 DriverSendToPort;
    importFunction3 WaitForChar;
    importFunction4 ClosePort;
    //load DLL file
    HINSTANCE hinstLib = LoadLibrary("VxmDriver.dll");
    if (hinstLib == NULL) {
                printf("ERROR: unable to load DLL\n");
                getch();
                return 1;
                }
    // Get OpenPort pointer
    OpenPort = (importFunction1)GetProcAddress (hinstLib, "OpenPort");
    if (OpenPort == NULL) {
                          printf("ERROR: unalbe to find OpenPort\n");
                          getch();
                          FreeLibrary(hinstLib); 
                          return 1; 
                          }
    // Get DriverSendToPort pointer
    DriverSendToPort = (importFunction2)GetProcAddress (hinstLib, "DriverSendToPort");
    if (DriverSendToPort == NULL) {
                          printf("ERROR: unalbe to find DriverSendToPort\n");
                          getch();
                          FreeLibrary(hinstLib); 
                          return 1; 
                          }
    // Get WaitForChar pointer
    WaitForChar = (importFunction3)GetProcAddress (hinstLib, "WaitForChar");
    if (WaitForChar == NULL) {
                          printf("ERROR: unalbe to find WaitForChar\n");
                          getch();
                          FreeLibrary(hinstLib); 
                          return 1; 
                          }       
    // Get ClosePort pointer
    ClosePort = (importFunction4)GetProcAddress (hinstLib, "ClosePort");
    if (ClosePort == NULL) {
                          printf("ERROR: unalbe to find ClosePort\n");
                          getch();
                          FreeLibrary(hinstLib); 
                          return 1; 
                          }
    printf("All files have loaded successfully.\nHit any key to enter program.\n");
    getch();
    //Run all functions and free library/print statement on success...
    OpenPort(2,9600);
    for ( a = 0 ; a < 10 ; a++ ) {
        if ( a > 0 ) {
            DriverSendToPort("C,I1M400,R,");
              WaitForChar("^",0);
            }
        for ( b = 0; b < 10; b++ ) {
            DriverSendToPort("F,C,I2M400,R,");
            WaitForChar("^",0);
            }
        DriverSendToPort("C,I2M-4000,R,");
        WaitForChar("^",0);
        }
    DriverSendToPort("C,I1M-4000,R,");
    WaitForChar("^",0);
    DriverSendToPort("Q,");
    ClosePort();
    FreeLibrary(hinstLib);
    printf("successfully completed");
    getch();
    return 0;
}

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1. your function signatures are char* and not const char* - Are you sure that your dll functions do not try to modify incoming buffers?
2. You do not wait till the last string sent to the port is actually sent before closing the port - are you sure that the function sending buffer is working synchroneously? Try to sleep for 2000 ms before Closing the port, for example...

I changed it to const char* and that didn't help. It still has a segfault error. Also, i already have tried adding a "pause" into the program. I had it at 10 sec and it still errors out after four commands.

All those functions return a value (apparently), which you're ignoring.

You don't free some of your resources when an error occurs while loading resources.

Code:

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    HINSTANCE hinstLib = LoadLibrary("VxmDriver.dll");
    if (hinstLib == NULL) {
                printf("ERROR: unable to load DLL\n");
                getch();
                return 1;
                }
    // Get OpenPort pointer
    OpenPort = (importFunction1)GetProcAddress (hinstLib, "OpenPort");
    if (OpenPort == NULL) {
        /* shouldn't you close hinstLib here? */
                          printf("ERROR: unalbe to find OpenPort\n");
                          getch();
                          FreeLibrary(hinstLib); 
                          return 1; 
                          }
    // Get DriverSendToPort pointer
    DriverSendToPort = (importFunction2)GetProcAddress (hinstLib, "DriverSendToPort");
    if (DriverSendToPort == NULL) {
        /* shouldn't you close hinstLib here? */
        /* shouldn't you close OpenPort here? */
                          printf("ERROR: unalbe to find DriverSendToPort\n");
                          getch();
                          FreeLibrary(hinstLib); 
                          return 1; 
                          }
        /* etc */

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At the very least you should call ClosePort() when the resource loadings after the port has been opened fail.