Why can't I get FormatMessage to load my resource string?

Raymond Chen

A common mistake I see is people confusing message tables with string resources. This basically shows up in one place: FormatMessage.

The folks who were designing Win32 decided that plain string resources weren’t fancy enough, so they invented message tables, which is just another way of storing strings in resources. Why string resources weren’t good enough I don’t know.

The FormatMessage function accepts a message number, which is looked up in a message table, not in a string resource. In other words, if you have something like this:

#define IDS_MYMESSAGE 100
    IDS_MYMESSAGE "Hello, %1"
TCHAR szBuffer[256];
FormatMessage(FORMAT_MESSAGE_FROM_HMODULE, g_hInstance,
              IDS_MYMESSAGE, 0, szBuffer, 256, Arguments);

the call to FormatMessage will fail because you passed in a string resource identifier, not a message identifier. Since nobody actually uses message tables, you almost certainly want to pass the FORMAT_MESSAGE_FROM_STRING flag.

TCHAR szMessage[256];
LoadString(g_hInstance, IDS_MYMESSAGE, szMessage, 256);
TCHAR szBuffer[256];
FormatMessage(FORMAT_MESSAGE_FROM_STRING, szMessage,
              IDS_MYMESSAGE, 0, szBuffer, 256, Arguments);

The only place you will normally want to format a message from a message table is when you want to access the system message table to get the text associated with an error code. (But don’t forget the FORMAT_MESSAGE_IGNORE_INSERTS flag!)