gdbのptypeを使うのが簡単。 例えば、以下のfoo.c。 #include <sys/types.h> struct st { int i; char c; }; typedef int Array[10]; typedef struct st St; int main(void) { size_t s1; ssize_t s2; pid_t pid; Array arr; St st1; return 0; } $ gcc -Wall -g -o foo foo.c $ gdb foo (gdb) b main (gdb) run (gdb) ptype s1 type = long unsigned int (gdb) ptype size_t type = long unsigned int (gdb) ptype s2 type = long int (gdb) ptype