segfault追加空字符串C

我正在尝试附加一个带有特定字符的字符串。我得到了一个segfault,我认为这是因为我试图附加到一个内存地址,我不知道我将如何改变这个。

这是调试时显示的错误,

打印:6

附加字:ZHE

分段故障(堆芯倾倒)

这是对应于segfault的代码

void append(char* s, char c){

        printf("print: 5\n");
        int len = strlen(s);

        printf("print: 6\n");
        printf("word to be appended: %s\n", s);
        s[len] = c;

        printf("print: 7\n");
        s[len+1] = '\0';
}

这是对上述函数的调用,位于这组代码的底部,带有相应的变量初始化

    int x;
    char *tempLine = NULL;
    char *token = NULL;
    char *punctuationChar;
    size_t length = 0;
    int charCount = 0;
    char *word;
    int i;
    int p;
    int check = 0;
    struct node *curr = NULL;
    struct node *newNode = NULL;

    (*head) = malloc(sizeof(struct node));   
    curr = (*head);     

    rewind(stream);

    for(x = 0; x < size; x++){

            getline(&tempLine, &length, stream);
            token = strtok(tempLine, " ");
            if(x == 0){

                    charCount = strlen(token);
                    curr -> word = malloc(charCount *(sizeof (char)) + 1);
                    strcpy(curr -> word, token);
                    token = strtok(NULL, " ");

            }else{   

            while(token != "\n"){

                    check = 0;
                    printf("token: %s\n", token);
                    charCount = strlen(token);
                    printf("print: 1\n");

                    //check for punctuation aka, last word on line
                    for(i = 0; i < charCount; i++){
                            printf("iteration: %d\n", x);
                            if(ispunct(token[i])){

                                    printf("print: 2\n");
                                    append(punctuationChar, token[i]);
                                    check = 1;