/**************************************************************************** * libs/libc/string/lib_strstr.c * * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. The * ASF licenses this file to you 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 * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations * under the License. * ****************************************************************************/ /**************************************************************************** * Included Files ****************************************************************************/ #include <nuttx/config.h> #include <string.h> /**************************************************************************** * Public Functions ****************************************************************************/ FAR char *strstr(FAR const char *str, FAR const char *substr) { FAR const char *candidate; /* Candidate in str with matching start character */ char ch; /* First character of the substring */ size_t len; /* The length of the substring */ /* Special case the empty substring */ len = strlen(substr); ch = *substr; if (!ch) { /* We'll say that an empty substring matches at the beginning of * the string */ return (FAR char *)str; } /* Search for the substring */ candidate = str; for (; ; ) { /* strchr() will return a pointer to the next occurrence of the * character ch in the string */ candidate = strchr(candidate, ch); if (!candidate || strlen(candidate) < len) { /* First character of the substring does not appear in the string * or the remainder of the string is not long enough to contain the * substring. */ return NULL; } /* Check if this is the beginning of a matching substring */ if (strncmp(candidate, substr, len) == 0) { return (FAR char *)candidate; } /* No, find the next candidate after this one */ candidate++; } /* Won't get here, but some compilers might complain. Other compilers * might complain about this code being unreachable too. */ return NULL; }