C程序中的分段故障错误

Question

我认为分割错误与不正确使用内存有关。我检查了变量引用，但似乎无法发现给我分割错误的问题。我认为在函数2中添加其他字符时，可能与for循环中字符/字符串的无效使用有关。

//ISBN.cpp
#include <iostream>
#include <iomanip>
#include <cstring>
#include <stdio.h>
#include <stdlib.h>

using namespace std;
#include "ISBN.h"

//validates the isbn string
int isValid(const char str[]){
    bool valid = false;
    int sum = 0;
    int i, j = 10;
    if(str != NULL){
        for(i=0; i<=9; i++){
            sum += (str[i]-'0')*j;
            //cout << "str[i]-'0' : " << (str[i]-'0')*j <<  endl;
            //cout << "sum : " <<sum <<  endl;
            j--;
        }
        //cout << sum << endl;
        if(sum % 11 == 0){
            valid = true;
        }
    }
    return valid;
}

//checks if isbn is a registered number
int isRegistered(FILE* fp, const char str[], char area[], char publisher[], char title[]){

    bool isregister = false;
    bool farea = false;
    bool fpub = false;

    char areatmp[5] = {0};
    char pubtmp[8] = {0};
    char titletmp[7] = {0};

    int len;
    int lenpub;
    int lentitle;
    int areano;
    int pospub, postitle;

    for(int i=0; i < 5 && farea == 0; i++){
        len = strlen(areatmp);
        areatmp[len] = str[i];
        areatmp[len+1] = '\0';
        areano = atoi(areatmp);
        farea = isRegistered(fp,areano);
        pospub = i + 1;
    }

    strcpy(area,areatmp);

    if(farea != false){
        for(int i = pospub; i <= 8 && fpub == false; i++){
            lenpub = strlen(pubtmp);
            pubtmp[lenpub] = str[i];
            pubtmp[lenpub+1] = '\0';
            //cout << "---------------------------------------" << endl;
            //cout << "pubtmpdigit : " << pubtmp << endl;
            fpub = isRegistered(fp,atoi(area),pubtmp);
            postitle = i + 1;
        }

        isregister = fpub;

        for(int i = postitle; i <= 8; i++){
            lentitle = strlen(titletmp);
            titletmp[lentitle] = str[i];
            titletmp[lentitle+1] = '\0';
        }
    }
    strcpy(publisher, pubtmp);
    strcpy(title, titletmp);
    //cout << "title ---->" << titletmp << endl;
    return isregister;
}