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// Copyright 2017 The Abseil Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// These routines provide mem versions of standard C string routines,
// such as strpbrk. They function exactly the same as the str versions,
// so if you wonder what they are, replace the word "mem" by
// "str" and check out the man page. I could return void*, as the
// strutil.h mem*() routines tend to do, but I return char* instead
// since this is by far the most common way these functions are called.
// The difference between the mem and str versions is the mem version
// takes a pointer and a length, rather than a '\0'-terminated string.
// The memcase* routines defined here assume the locale is "C"
// (they use absl::ascii_tolower instead of tolower).
// These routines are based on the BSD library.
// Here's a list of routines from string.h, and their mem analogues.
// Functions in lowercase are defined in string.h; those in UPPERCASE
// are defined here:
// strlen --
// strcat strncat MEMCAT
// strcpy strncpy memcpy
// -- memccpy (very cool function, btw)
// -- memmove
// -- memset
// strcmp strncmp memcmp
// strcasecmp strncasecmp MEMCASECMP
// strchr memchr
// strcoll --
// strxfrm --
// strdup strndup MEMDUP
// strrchr MEMRCHR
// strspn MEMSPN
// strcspn MEMCSPN
// strpbrk MEMPBRK
// strtok --
// strprefix MEMPREFIX (strprefix is from strutil.h)
// strcaseprefix MEMCASEPREFIX (strcaseprefix is from strutil.h)
// strsuffix MEMSUFFIX (strsuffix is from strutil.h)
// strcasesuffix MEMCASESUFFIX (strcasesuffix is from strutil.h)
// -- MEMIS
// strcount MEMCOUNT (strcount is from strutil.h)
#include <cstddef>
#include <cstring>
#include "absl/base/port.h" // disable some warnings on Windows
#include "absl/strings/ascii.h" // for absl::ascii_tolower
namespace absl {
namespace strings_internal {
inline char* memcat(char* dest, size_t destlen, const char* src,
size_t srclen) {
return reinterpret_cast<char*>(memcpy(dest + destlen, src, srclen));
int memcasecmp(const char* s1, const char* s2, size_t len);
char* memdup(const char* s, size_t slen);
char* memrchr(const char* s, int c, size_t slen);
size_t memspn(const char* s, size_t slen, const char* accept);
size_t memcspn(const char* s, size_t slen, const char* reject);
char* mempbrk(const char* s, size_t slen, const char* accept);
// This is for internal use only. Don't call this directly
template <bool case_sensitive>
const char* int_memmatch(const char* haystack, size_t haylen,
const char* needle, size_t neelen) {
if (0 == neelen) {
return haystack; // even if haylen is 0
const char* hayend = haystack + haylen;
const char* needlestart = needle;
const char* needleend = needlestart + neelen;
for (; haystack < hayend; ++haystack) {
char hay = case_sensitive
? *haystack
: absl::ascii_tolower(static_cast<unsigned char>(*haystack));
char nee = case_sensitive
? *needle
: absl::ascii_tolower(static_cast<unsigned char>(*needle));
if (hay == nee) {
if (++needle == needleend) {
return haystack + 1 - neelen;
} else if (needle != needlestart) {
// must back up haystack in case a prefix matched (find "aab" in "aaab")
haystack -= needle - needlestart; // for loop will advance one more
needle = needlestart;
return nullptr;
// These are the guys you can call directly
inline const char* memstr(const char* phaystack, size_t haylen,
const char* pneedle) {
return int_memmatch<true>(phaystack, haylen, pneedle, strlen(pneedle));
inline const char* memcasestr(const char* phaystack, size_t haylen,
const char* pneedle) {
return int_memmatch<false>(phaystack, haylen, pneedle, strlen(pneedle));
inline const char* memmem(const char* phaystack, size_t haylen,
const char* pneedle, size_t needlelen) {
return int_memmatch<true>(phaystack, haylen, pneedle, needlelen);
inline const char* memcasemem(const char* phaystack, size_t haylen,
const char* pneedle, size_t needlelen) {
return int_memmatch<false>(phaystack, haylen, pneedle, needlelen);
// This is significantly faster for case-sensitive matches with very
// few possible matches. See unit test for benchmarks.
const char* memmatch(const char* phaystack, size_t haylen, const char* pneedle,
size_t neelen);
} // namespace strings_internal
} // namespace absl