为什么我的代码无法正常工作？某些行无法执行

Question

在此程序中，我需要读取文件并进行一些计算。问题是带有注释的行未运行。事件printf。所有其他if条件也可以完美运行，但不是第一个if条件及其上方的printf。无论我在标记行之间写什么，都行不通。有解决方案吗？

#include<stdio.h>
#include<stdbool.h>
#include<stdlib.h>
#include<string.h>


int main(void){

    double total=0,max_sale=0,min_sale=0,sale,Southern=0,Western=0,Uva=0,North=0,Eastern=0,Central=0,NorthWest=0,NorthC=0,Sabaragamu=0;
    int sales_n=0;
    char ID_no[15],max_ID[15],min_ID[15];
    char E_name[20],E_tp[10],address[100],province[10],temp[100],name2[20],province2[10];
    bool flag = true,flag2,exsist=false;

    FILE * dataP;
    FILE * saleP;

    saleP = fopen("sales.txt","r");

    if(saleP==NULL){
            printf("Error: Unable to open file\n");
            exit(1);
        }


    while(true){

        dataP = fopen("employee_data.dat","r");
        if(dataP==NULL){
            printf("Error: Unable to open file\n");
            exit(1);
        }

        fscanf(saleP," %s %lf",ID_no,&sale);
        if(feof(saleP)){
            break;
        }
/******************************************************************************************************/
        while(!feof(dataP)){

           fscanf(dataP," %s",temp);

           fscanf(dataP," %s",E_name);
           strcpy(name2,E_name);
           fscanf(dataP," %s",E_tp);
           fscanf(dataP," %s",address);
           fscanf(dataP," %s",province);

           strcpy(province2,strupr(province));
           printf("\nnew province %s",province2);

           if(!strcmp(temp,ID_no)){


            printf("ID no = %s   temp = %s\n",ID_no,temp);



            printf("%s\n",province2);          //form this line

            if(!strcmp(province2,"SOUTHERN")){
                Southern +=sale;
                printf("Passsed\n");
            }                                 //to this line doesn't execute



            else if(!strcmp(province2,"WESTERN")){
                Western +=sale;
            }

            else if(!strcmp(province2,"CENTRAL")){
                Central +=sale;
            }

            else if(!strcmp(province2,"NORTHWEST")){
                NorthWest +=sale;
            }

            else if(!strcmp(province2,"NORTHCENTRAL")){
                NorthC +=sale;
            }

            else if(!strcmp(province2,"EASTERN")){
                Eastern +=sale;
            }

            else if(!strcmp(province2,"SABARAGAMU")){
                Sabaragamu +=sale;
            }

            else if(!strcmp(province2,"NORTHEN")){
                North +=sale;
            }

            else if(!strcmp(province2,"UVA")){
                Uva +=sale;
            }

           }


        }



        printf("ID %s   sale %.2lf\n",ID_no,sale);

        total+=sale;
        sales_n++;

        if(sales_n==1){
            max_sale=sale;
            min_sale=sale;
            strcpy(max_ID,ID_no);
            strcpy(min_ID,ID_no);

        }

        if(max_sale<sale){
            max_sale=sale;
            strcpy(max_ID,ID_no);
        }
        else if(min_sale>sale){
            min_sale=sale;
            strcpy(min_ID,ID_no);
        }


    }

    //printf("\ntotal is : %.2lf\n max sell is %.2lf\n min sell is %.2lf\n total sales number is %d",total,max_sale,min_sale,sales_n);

    //printf("\nmax seller is %s\nMin seller is %s",max_ID,min_ID);

    printf("\n ==============================================================\n");
    printf("             S H O W I N G    S U M M A R R Y");
    printf("\n ==============================================================\n");

    printf("\n     > Total sales       : Rs.%.2lf\n",total);
    printf("\n     > Total sales count : %d\n",sales_n);
    printf("\n     > Top seller        : %s\n",max_ID);
    printf("\n     > Top sale          : Rs.%.2lf\n",max_sale);
    printf("\n     > Weakest seller    : %s\n",min_ID);
    printf("\n     > Weakest sale      : Rs.%.2lf\n",min_sale);



    printf("\n\n\n %.2lf\n %.2lf\n %.2lf\n %.2lf\n %.2lf\n %.2lf\n %.2lf\n %.2lf\n %.2lf\n",Southern,Western,Uva,North,Eastern,Central,NorthWest,NorthC,Sabaragamu);



}

Answer 1

其中一个文件可能因为不存在而无法打开。

在代码中添加以下几行：

....
saleP = fopen("sales.txt","r");
if (saleP == NULL)  //<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
{
   printf("can't open file \n");
   exit(1);
} 

while(true){
    dataP = fopen("employee_data.dat","r");
    if (dataP == NULL)  // <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    {
       printf("can't open file \n");
       exit(1);
    } 
    fscanf(saleP," %s %lf",ID_no,&sale);
    ....

如果由于某种原因无法打开文件，则

fopen返回NULL。如果不进行检查，则程序将继续执行并尝试对该NULL文件指针执行其他文件操作，并且对NULL文件指针进行文件操作会导致undefined behaviour，这基本上意味着一切都会发生，主要是奇怪的错误和其他不可预测的行为。