獲取子字符串的索引

Question

我有char * source，我想從中提取subsrting，我知道從符號「abc」開始，並在源結束處結束。與strstr我可以得到poiner，但不是位置，沒有位置，我不知道子字符串的長度。我怎樣才能得到純C的子字符串的索引？

Answer 1

使用指針減法。

char *str = "sdfadabcGGGGGGGGG"; 
char *result = strstr(str, "abc"); 
int position = result - str; 
int substringLength = strlen(str) - position; 

Answer 2

newptr - source會給你抵消。

Answer 3

如果你有指向字符串的第一個字符，和子在源字符串的結尾結束，則：

• strlen(substring)會給你它的長度。
• substring - source會給你開始索引。

Answer 4

char *source = "XXXXabcYYYY"; 
char *dest = strstr(source, "abc"); 
int pos; 

pos = dest - source; 

Answer 5

形式上，其它的是正確的 - substring - source確實開始索引。但是你不需要它：你可以使用它作爲source的索引。因此，編譯器計算source + (substring - source)作爲新地址 - 但只有substring對於幾乎所有用例都足夠了。

只是提示優化和簡化。

Answer 6

的開始和結束字

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 
    } 

Answer 7

這裏切一個字一個字符串的函數是有偏移的特徵對strpos函數的C版...

#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; 
}