strchr

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I am learning SIMD and was curious to see whether it was possible to beat strchr at finding a character. It appears that strchr uses the same intrinsics but I assume that it checks for a null, whereas I know the character is in the array and plan on avoiding a null check. My code is: size_t N = 1e9; bool found = false; //Not really used ... size_t char_index1 = 0; size_t char_index2 = 0; char * str = malloc(N); memset(str,'a',N); __m256i char_match; __m256i str_simd; __m256i result; __m256i* pSrc1; int simd_mask; str[(size_t)5e8] = 'b'; char

#include<stdio.h> #include<stdlib.h> #include<string.h> char *mystrchr(char *str, char c) { int i; for (i = 0; i<strlen(str); i++) { if (*(str + i) == c) { return str + i; } } return NULL; } int main() { char *str = "abcdef"; char c = 's'; char *fin = mystrchr(str, c); printf("%s", fin); system("pause"); return 0; }

Suppose I have a string "qwerty" and I wish to find the index position of the e character in it. (In this case the index would be 2 ) How do I do it in C? I found the strchr function but it returns a pointer to a character and not the index. wj32 Just subtract the string address from what strchr returns: char *string = "qwerty"; char *e; int index; e = strchr(string, 'e'); index = (int)(e - string); Note that the result is zero based, so in above example it will be 2. You can also use strcspn(string, "e") but this may be much slower since it's able to handle searching for multiple possible

I tried to write my own implementation of the strchr() method. It now looks like this: char *mystrchr(const char *s, int c) { while (*s != (char) c) { if (!*s++) { return NULL; } } return (char *)s; } The last line originally was return s; But this didn't work because s is const. I found out that there needs to be this cast (char *), but I honestly don't know what I am doing there :( Can someone explain? I believe this is actually a flaw in the C Standard's definition of the strchr() function. (I'll be happy to be proven wrong.) (Replying to the comments, it's arguable whether it's really a