類似於PHP的子字符串函數C

Question

我一直在C中創建字符串（char *）操作函數，我最近的一個是PHP類的子字符串函數。我發佈信息以便其他人可以從中受益，對於有關改進功能的任何建議，我將不勝感激。

Answer 1

這裏是C.

char *substr(char *str, int start, int num) 
{ 
    //find string length 
    int len = sj_strlen(str); 

    char *result; 

    //Return "" if start is longer than str 
    if(start > len || (start*-1) > len) 
    { 
     result = malloc(1); 
     *result = '\0'; 
     return result; 
    } 

    //Setting pointer to appropriate position 
    if(start >= 0) 
    { 
     str += start; 
    } 
    else 
    { 
     str += (len+start); 
    } 

    //Allocate space for returned substring 
    result = malloc(num+1); 
    char *ptr = result; 

    //Adding characters to the result 
    while(num > 0 && *str) 
    { 
     *ptr++ = *str++; 
     num--; 
    } 

    //Terminating character 
    *ptr = '\0'; 

    return result; 
} 

int main() 
{ 
    char *str = "Hello, world!"; 
    printf("%s\n",substr(str,-10,2)); //outputs lo 
    printf("%s",substr(str,7,5)); //outputs world 
}