When you compile with -std=c89 , the Oracle Solaris Studio C compiler includes the data types long long and unsigned long long, which are similar to the data type long. The long long data type stores 64 bits of information; long stores 32 bits of information when compiling with -m32. The long data type stores 64 bits when compiling with -m64. The long long data type is not available in -std=c89 -pedantic (a warning is issued).