C语言 获取子串的索引
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Get index of substring
提问by Country
I have char * source, and I want extract from it subsrting, that I know is beginning from symbols "abc", and ends where source ends. With strstrI can get the poiner, but not the position, and without position I don't know the length of the substring. How can I get the index of the substring in pure C?
我有char * source，我想从中提取 subsrting，我知道它从符号“abc”开始，并在 source 结束的地方结束。使用strstr我可以获得指针，但不能获得位置，没有位置我不知道子字符串的长度。如何在纯 C 中获取子字符串的索引？
回答by Robert S. Barnes
Use pointer subtraction.
使用指针减法。
char *str = "sdfadabcGGGGGGGGG";
char *result = strstr(str, "abc");
int position = result - str;
int substringLength = strlen(str) - position;
回答by mkb
newptr - sourcewill give you the offset.
newptr - source会给你抵消。
回答by KevinDTimm
char *source = "XXXXabcYYYY";
char *dest = strstr(source, "abc");
int pos;
pos = dest - source;
回答by Howard J
Here is a C version of the strpos function with an offset feature...
这是具有偏移功能的 strpos 函数的 C 版本...
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int strpos(char *haystack, char *needle, int offset);
int main()
{
char *p = "Hello there all y'al, hope that you are all well";
int pos = strpos(p, "all", 0);
printf("First all at : %d\n", pos);
pos = strpos(p, "all", 10);
printf("Second all at : %d\n", pos);
}
int strpos(char *hay, char *needle, int offset)
{
char haystack[strlen(hay)];
strncpy(haystack, hay+offset, strlen(hay)-offset);
char *p = strstr(haystack, needle);
if (p)
return p - haystack+offset;
return -1;
}
回答by Graham Borland
If you have the pointer to the first char of the substring, and the substring ends at the end of the source string, then:
如果您有指向子字符串第一个字符的指针，并且子字符串在源字符串的末尾结束，则：
strlen(substring)will give you its length.substring - sourcewill give you the start index.
strlen(substring)会给你它的长度。substring - source会给你开始索引。
回答by glglgl
Formally the others are right - substring - sourceis indeed the start index. But you won't need it: you would use it as index into source. So the compiler calculates source + (substring - source)as the new address - but just substringwould be enough for nearly all use cases.
正式其他人是对的 -substring - source确实是开始索引。但是您不需要它：您可以将其用作source. 所以编译器计算source + (substring - source)为新地址 - 但substring对于几乎所有用例来说就足够了。
Just a hint for optimization and simplification.
只是优化和简化的提示。
回答by StrongLucky
A function to cut a word out out of a string by a start and end word
通过开始和结束单词从字符串中切出单词的函数
string search_string = "check_this_test"; // The string you want to get the substring
string from_string = "check"; // The word/string you want to start
string to_string = "test"; // The word/string you want to stop
string result = search_string; // Sets the result to the search_string (if from and to word not in search_string)
int from_match = search_string.IndexOf(from_string) + from_string.Length; // Get position of start word
int to_match = search_string.IndexOf(to_string); // Get position of stop word
if (from_match > -1 && to_match > -1) // Check if start and stop word in search_string
{
result = search_string.Substring(from_match, to_match - from_match); // Cuts the word between out of the serach_string
}
