c语言怎么从字符串中提取字符串

?C???,?????????sscanf()?????????????????????????sscanf()???????:

#include 

int main() {
    char str[] = "Hello, World! This is a test string.";
    char subtr[20]; // ?????????
    int start_index = 7; // ?????????
    int length = 5; // ???????

    sscanf(str + start_index, " s", subtr); // ??????????????

    printf("The sub string is: %s\n", subtr);

    return 0;
}

??????,????sscanf()???str??????????7??????5??????

??????????????????,??????????:

#include 

void substring(char s[], int start, int len, char sub[]) {
    int i;
    for (i = 0; i < len && s[start + i] != '\0'; i++) {
        sub[i] = s[start + i];
    }
    sub[i] = '\0';
}

int main() {
    char str[] = "Hello, World! This is a test string.";
    char subtr[20]; // ?????????
    int start_index = 7; // ?????????
    int length = 5; // ???????

    substring(str, start_index, length, subtr);

    printf("The sub string is: %s\n", subtr);

    return 0;
}

???????????????substring()????????