Using snprintf to avoid buffer overruns

I am using snprintf like this to avoid a buffer overrun:

char err_msg[32] = {0};
snprintf(err_msg, sizeof(err_msg) - 1, "[ ST_ENGINE_FAILED ]");

I added the -1 to reserve space for the null terminator in case the string is more than 32 bytes long.

Am I correct in my thinking?

Platform:

• GCC 4.4.1
• C99