Using built-in functions to improve performance

A built-in function is inline code that is generated in place of an actual function call.

The built-in functions described in this topic behave exactly the same as those in the C library. The compiler will generate inline code for these functions if the appropriate header file is included in the source. For more information, see Built-in functions in z/OS XL C/C++ Runtime Library Reference.

If you have included the header files but you want to call either the library version of the function or your own version, enclose the function name in parentheses when you make the call. For example, if you wanted to call only memcpy from the header file and use the built-in functions for other memory-related functions, code the function call as follows:

(memcpy)(buf1, buf2, len)

Table 1. C-library built-in functions
Built-In Function	Header File
`abs()`	`stdlib.h`
`alloca()`	`stdlib.h`
`ceil()`	`math.h`
`ceilf()`	`math.h`
`ceill()`	`math.h`
Note: The compiler only attempts to generate inline code for `ceil()`, `ceilf()`, and `ceill()` when the `OPTIMIZE(2)` compiler option is used.
`decabs()`	`decimal.h`
`decchk()`	`decimal.h`
`decfix()`	`decimal.h`
`fabs()`	`math.h`
Note: The compiler only attempts to generate inline code for `fabs()` when the `OPTIMIZE(2)` compiler option is used.
`floor()`	`math.h`
`floorf()`	`math.h`
`floorl()`	`math.h`
Note: The compiler only attempts to generate inline code for `floor()`, `floorf()`, and `floorl()` when the `OPTIMIZE(2)` compiler option is used.
`fortrc()`	`stdlib.h`
`memchr()`	`string.h`
`memcpy()`	`string.h`
`memcmp()`	`string.h`
`memset()`	`string.h`
`strcat()`	`string.h`
`strchr()`	`string.h`
`strcmp()`	`string.h`
`strcpy()`	`string.h`
`strlen()`	`string.h`
`strncat()`	`string.h`
`strncmp()`	`string.h`
`strncpy()`	`string.h`
`strrchr()`	`string.h`
`wmemchr()`	`wchar.h`
`wmemcmp()`	`wchar.h`
`wmemcpy()`	`wchar.h`
`wmemset()`	`wchar.h`
Note: The compiler only attempts to generate inline code for `wmemchr()`, `wmemcmp()`, `wmemcpy()`, and `wmemset()` when the ARCH(7) compiler option is used. LP64 compiles will not generate inline code.