bcopy / bzero / index / rindex (3) - glibc

Split from the chapter glibc: strings, ctype and stdlib arithmetic into the per-function layout; see the method page and the glibc ledger for coverage status.

Declaration and gates

#include <strings.h>

void bcopy(const void *src, void *dest, size_t n);  /* args NOT like memcpy */
void bzero(void *s, size_t n);
char *index(const char *s, int c);                  /* == strchr */
char *rindex(const char *s, int c);                 /* == strrchr */

Declared in strings.h under __USE_MISC || !__USE_XOPEN2K8 (/usr/include/strings.h lines 32-99): visible in default builds, suppressed by strict POSIX macro sets. strings.h also declares bcmp under the same gate.

Semantics

bcopy copies n bytes from src to dest and handles overlapping areas like memmove; it returns nothing (bcopy(3)). bzero zeroes n bytes at s (bzero(3)). index/rindex are strchr/strrchr under their BSD names, terminator included (index(3)). All return no value (the two search functions return char *).

Gotchas and portability

• Argument-order trap: bcopy(src, dest, n) reverses the memcpy operand order; bcopy(3) CONFORMING TO explicitly warns “the first two arguments are interchanged for memcpy(3) and memmove(3)”. Translated code is the primary source of bcopy-induced corruption.
• Obsolescence is documented, not folkloric: POSIX.1-2001 marked all four LEGACY and POSIX.1-2008 removed their specifications, directing users to memcpy/memmove/memset/strchr/strrchr (bcopy(3), bzero(3), index(3) CONFORMING TO).
• bzero is memset(s, 0, n); but for secrets prefer explicit_bzero, which the compiler may not elide (bzero(3) page covers both).
• Header hygiene: in strict _POSIX_C_SOURCE >= 200809L builds glibc hides these declarations, so legacy code needs _DEFAULT_SOURCE (or its pre-2.19 _BSD_SOURCE) to compile (strings.h gate).
• nm alias evidence on this host: index shares the address of strchr (0x…a8080) and rindex of strrchr (0x…aa2a0), i.e. the BSD names are literal aliases, so there is no behavioral difference left.
• musl 1.2.5 keeps all four for compatibility (musl src/string/{bcopy,bzero,index,rindex}.c).

References

• glibc manual: string.texi (legacy BSD names appear in the copy and search nodes only as contrasts)
• man3: bcopy(3), bzero(3) (covers explicit_bzero), index(3) (covers rindex)
• header: /usr/include/strings.h
• symbols: nm -D --with-symbol-versions libc.so.6