WIN32 C-program with Windows Mobile 5.0 SDK : Unable to use time_t To Show Current Date and Time

Question

I am writing a WIN32 C-program for a Motorola MC-55A PDA using Windows Mobile 5.0 SDK. I'm trying to get the current date and time to get a DDMMYYYYHHMMSS unique string that I can use. I've checked the tutorials and tried to use time_t and SYSTEMTIME but its coming back with the error : " illegal use of this type as an expression" (see code below). I've included the required header files including "time.h" but the error persists with the use of time_t and SYSTEMTIME . Here is my code:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <windows.h>
#include <windowsx.h>

.
.
.
case WM_INITDIALOG:

//Below fails with error : 'time_t' : illegal use of this type as an expression  
//C:\Program Files (x86)\Windows Mobile 5.0 SDK R2\PocketPC\include\ARMV4I\stdlib.h : 
//see declaration of 'time_t
time_t current_time = time(NULL);
printf("Hours since January 1, 1970 = %ld\n", current_time/3600);

//This also fails
time_t now;
time(&now);


//SYSTEMTIME below also fails with error : 'SYSTEMTIME' : illegal use of this type as an expression  
//C:\Program Files (x86)\Windows Mobile 5.0 SDK R2\PocketPC\include\ARMV4I\winbase.h : 
//see declaration of 'SYSTEMTIME'
GetSystemTime(&st);
GetLocalTime(&lt);                  
printf("The system time is: %02d:%02d\n", st.wHour, st.wMinute);
printf(" The local time is: %02d:%02d\n", lt.wHour, lt.wMinute);

How do I get the current date and time?

Answer 1

A workaround is using GetSystemTime or/and GetLocalTime functions by first adding a pragma for Kernel32.lib where the 2 functions are defined at the very top of your code.

//This works

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <windows.h>
#include <windowsx.h>
#pragma comment(lib, "Kernel32.lib")

.
.
.
case WM_INITDIALOG:

     GetSystemTime(&st);
     GetLocalTime(&lt);                 
     printf("The system time is: %02d:%02d\n", st.wHour, st.wMinute);
     printf(" The local time is: %02d:%02d\n", lt.wHour, lt.wMinute);

Answer 2

Although you haven't posted your complete code, it appears that you are declaring the current_time, st and it variables in an incorrect/disallowed place (after case WM_INITDIALOG:). You should either declare these variables before the switch statement, or add enclosing { ... } braces inside that case.

For example, code like this is ill-formed:

switch (a) {
    case 1:
        int b = a/2; // illegal here!
        //...
        break;
    default:
        break;
}

but this will work:

int b; // Note: This declaration MAY need to be at the beginning of the enclosing function!
switch (a) {
    case 1:
        b = a/2; // works
        //...
        break;
    default:
        break;
}

and so will this:

switch (a) {
    case 1: { // These "{ ... }" create a new scope
        int b = a/2; // works
        //...
        break;
    }
    default:
        break;
}

The reason for this is that, in your code, the declaration/definition of the aforementioned variables is skipped by cases other than WM_INITDIALOG. See this Stack Overflow Q/A for further discussion: Why can't variables be declared in a switch statement?