link#

I’ll explain the key functions in glibc’s string.h header, categorized by their purpose:

Memory Operations#

Function	Purpose
`memcpy(dest, src, n)`	Copy n bytes from src to dest (regions MUST NOT overlap)
`memmove(dest, src, n)`	Copy n bytes from src to dest (handles overlapping regions safely)
`memset(dest, c, n)`	Fill n bytes with character c
`memcmp(s1, s2, n)`	Compare first n bytes of two memory blocks
`memchr(s, c, n)`	Find first occurrence of c in first n bytes
`memrchr(s, c, n)`	Find last occurrence of c in first n bytes (GNU extension)
`rawmemchr(s, c)`	Find c in string, assumes it exists (optimized)
`mempcpy(dest, src, n)`	Like memcpy but returns pointer after dest+n
`memccpy(dest, src, c, n)`	Copy until c found or n bytes
`memcmpeq(s1, s2, n)`	Memory comparison that returns 0/1 only

Function	Purpose
`strlen(s)`	Get string length (excluding null terminator)
`strnlen(s, maxlen)`	Get length up to maxlen (safe for non-null-terminated strings)
`strcpy(dest, src)`	Copy string (no bounds checking!)
`strncpy(dest, src, n)`	Copy up to n characters (may not null-terminate)
`strcat(dest, src)`	Append src to dest
`strncat(dest, src, n)`	Append up to n characters (always null-terminates)
`strcmp(s1, s2)`	Compare two strings
`strncmp(s1, s2, n)`	Compare first n characters
`strchr(s, c)`	Find first occurrence of c in string
`strrchr(s, c)`	Find last occurrence of c in string
`strchrnul(s, c)`	Like strchr but returns pointer to null if not found (GNU)
`strstr(haystack, needle)`	Find substring
`strcasestr(h, n)`	Case-insensitive substring search (GNU)
`strpbrk(s, accept)`	Find first char from accept set in s
`strspn(s, accept)`	Count initial chars from accept set
`strcspn(s, reject)`	Count initial chars NOT from reject set
`stpcpy(dest, src)`	Copy string, return pointer to null terminator
`stpncpy(dest, src, n)`	Copy up to n chars, return pointer to end
`strlcpy(dest, src, n)`	Copy with size limit, returns src length (BSD)
`strlcat(dest, src, n)`	Concatenate with size limit (BSD)

Function	Purpose
`strtok(s, delim)`	Split string into tokens (NOT thread-safe!)
`strtok_r(s, delim, saveptr)`	Reentrant version with state parameter
`strsep(stringp, delim)`	Alternative tokenizer (BSD/GNU)

Function	Purpose
`strdup(s)`	Duplicate string (mallocs new copy)
`strndup(s, n)`	Duplicate up to n characters

Function	Purpose
`strcasecmp(s1, s2)`	Case-insensitive string compare
`strncasecmp(s1, s2, n)`	Case-insensitive compare of first n chars
`strcasecmp_l(s1, s2, loc)`	Locale-aware version
`strncasecmp_l(s1, s2, n, loc)`	Locale-aware version

Function	Purpose
`strverscmp(s1, s2)`	Compare version strings (e.g., “file1” < “file10”)
`strcoll(s1, s2)`	Locale-aware string comparison
`strxfrm(s, s2, n)`	Transform string for locale-aware comparison

Function	Purpose
`basename(path)`	Get final component of path

Function	Purpose
`ffs(i)`	Find first set bit (1-indexed position)

Function	Purpose
`__memcpy_chk`	Buffer overflow checked memcpy (Fortify)
`__memmove_chk`	Buffer overflow checked memmove
`__memset_chk`	Buffer overflow checked memset
`__strcpy_chk`	Buffer overflow checked strcpy
`__strcat_chk`	Buffer overflow checked strcat
`explicit_bzero(buf, len)`	Zero memory that won’t be optimized away
`memset_explicit(buf, c, len)`	Like explicit_bzero but with any value

Function	Purpose
`bzero(s, n)`	Zero n bytes (deprecated, use memset)

__ prefix = Internal glibc functions (__memcpy, __strlen, etc.)
_chk suffix = Runtime buffer overflow checking (FORTIFY_SOURCE)
_r suffix = Reentrant (thread-safe) versions
_l suffix = Locale-aware versions
libc_hidden_proto = Optimization - hides symbols for faster internal calls

This is the foundation of C string manipulation - virtually every C program uses these functions!