extern variable declaration not interchangeable to another c file?

Markel Robregado

Hi,

At my main. c file, I have these below variable declarations.

/*
* GLOBAL VARIABLES -- Start
*/
_u32 g_Status = 0;
_u32 g_PingPacketsRecv = 0;
_u32 g_GatewayIP = 0;
_u32 ui32SysClock;

At my cloud_demo.c I declare g_Status and ui32SysClock as "extern" to make these variables visible to all c files.

extern unsigned long ui32SysClock;
extern unsigned long g_Status;

If I declare these variables as extern at main c file instead. the g_Status variable cause this error bellow. But the ui32SysClock variable does not cause any error. Why is that? This error is sort of weird.

Description Resource Path Location Type
#10056 symbol "g_Status" redefined: first defined in "./cloud_demo.obj"; redefined in "./main.obj" wlan_station_exosite_write_read C/C++ Problem

- kel

over 9 years ago

0 George Mock over 9 years ago

TI__Guru**** 249680 points

Markel Robregado said:
At my cloud_demo.c I declare g_Status and ui32SysClock as "extern" to make these variables visible to all c files.

It doesn't work that way. extern declarations are usually in a header file, and this header file is included by all the C files. Please see this article (not from TI) for a full discussion.

Markel Robregado said:
symbol "g_Status" redefined: first defined in "./cloud_demo.obj"; redefined in "./main.obj"

Carefully search both files for g_Status. You will find definitions (not just declarations) in both of them. One of them must be removed.

Thanks and regards,

-George

0 Markel Robregado over 9 years ago in reply to George Mock

Guru 86755 points

Thanks, for your wisdom, George.

- kel

0 Douglas Gwyn over 9 years ago in reply to George Mock

Expert 2210 points

Also, _u32 might not be the same type as unsigned long, even if they have the same length.

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extern variable declaration not interchangeable to another c file?