函数memstr
大家用了memchr、strchr、strstr之后,有没有想要一个叫memstr的函数?从内存里面找特定的字符串?
glibc里面没有提供memstr,我这里提供一个吧。验证过的可靠版本:
[cpp]
//find 'substr' from a fixed-length buffer
//('full_data' will be treated as binary data buffer)
//return NULL if not found
char* memstr(char* full_data, int full_data_len, char* substr)
{
if (full_data == NULL || full_data_len <= 0 || substr == NULL) {
return NULL;
}
if (*substr == '\0') {
return NULL;
}
int sublen = strlen(substr);
int i;
char* cur = full_data;
int last_possible = full_data_len - sublen + 1;
for (i = 0; i < last_possible; i++) {
if (*cur == *substr) {
//assert(full_data_len - i >= sublen);
if (memcmp(cur, substr, sublen) == 0) {
//found
return cur;
}
}
cur++;
}
return NULL;
}
//find 'substr' from a fixed-length buffer
//('full_data' will be treated as binary data buffer)
//return NULL if not found
char* memstr(char* full_data, int full_data_len, char* substr)
{
if (full_data == NULL || full_data_len <= 0 || substr == NULL) {
return NULL;
}
if (*substr == '\0') {
return NULL;
}
int sublen = strlen(substr);
int i;
char* cur = full_data;
int last_possible = full_data_len - sublen + 1;
for (i = 0; i < last_possible; i++) {
if (*cur == *substr) {
//assert(full_data_len - i >= sublen);
if (memcmp(cur, substr, sublen) == 0) {
//found
return cur;
}
}
cur++;
}
return NULL;
}
这个函数调用了memcmp,应该可以利用memcmp的加速能力。
ps:研究过memcmp的同学应该都知道,memcmp会针对硬件做优化,比如一次比较多个字节什么的。
补充:软件开发 , C++ ,