什么功能从C中的字符串替换子字符串? [英] What function is to replace a substring from a string in C?

问题描述

给出一个( char * )字符串，我想查找所有出现的子字符串并将其替换为备用字符串.我没有在< string.h> .

Given a (char *) string, I want to find all occurrences of a substring and replace them with an alternate string. I do not see any simple function that achieves this in <string.h>.

推荐答案

优化器应消除大多数局部变量.使用tmp指针可以确保strcpy不必遍历字符串即可找到null.tmp指向每次调用后结果的结尾.(请参阅绘画家的施莱米尔(Schlemiel)，以了解为什么strcpy会令人讨厌.)

The optimizer should eliminate most of the local variables. The tmp pointer is there to make sure strcpy doesn't have to walk the string to find the null. tmp points to the end of result after each call. (See Shlemiel the painter's algorithm for why strcpy can be annoying.)

// You must free the result if result is non-NULL.
char *str_replace(char *orig, char *rep, char *with) {
    char *result; // the return string
    char *ins;    // the next insert point
    char *tmp;    // varies
    int len_rep;  // length of rep (the string to remove)
    int len_with; // length of with (the string to replace rep with)
    int len_front; // distance between rep and end of last rep
    int count;    // number of replacements

    // sanity checks and initialization
    if (!orig || !rep)
        return NULL;
    len_rep = strlen(rep);
    if (len_rep == 0)
        return NULL; // empty rep causes infinite loop during count
    if (!with)
        with = "";
    len_with = strlen(with);

    // count the number of replacements needed
    ins = orig;
    for (count = 0; tmp = strstr(ins, rep); ++count) {
        ins = tmp + len_rep;
    }

    tmp = result = malloc(strlen(orig) + (len_with - len_rep) * count + 1);

    if (!result)
        return NULL;

    // first time through the loop, all the variable are set correctly
    // from here on,
    //    tmp points to the end of the result string
    //    ins points to the next occurrence of rep in orig
    //    orig points to the remainder of orig after "end of rep"
    while (count--) {
        ins = strstr(orig, rep);
        len_front = ins - orig;
        tmp = strncpy(tmp, orig, len_front) + len_front;
        tmp = strcpy(tmp, with) + len_with;
        orig += len_front + len_rep; // move to next "end of rep"
    }
    strcpy(tmp, orig);
    return result;
}

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