Question

我的程序必须做两件事：输入一个点并输出最多四个点。该文件只能打开一次。但如果我想读点，没有任何事情发生。我做错了什么？

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

#define file "datei.dat"

struct{
   float x;
   float y;
   float z;
}point;

void output(FILE *save){
   while(fread(&point, sizeof(point), 4, save) != 4){
      printf("x-coordinatee: %f",point.x);
      printf("y-coordinate: %f",point.y);
      printf("z-coordinate: %f",point.z);
      printf("\n\n");
   }
   fclose(save);
}
void input(FILE *save){
     printf("x-coordinate:");
     scanf("%f", &point.x);
     printf("y-coordinate:");
     scanf("%f", &point.y);
     printf("z-coordinate:");
     scanf("%f", &point.z);

     fseek(save, 0, SEEK_END);
     if(fwrite(&point, sizeof(point), 1, save) != 1){
     fprintf(stderr, "Error...!!!\n");
     return;
     }
}

int main(void){
   char choice;

   FILE *save;
   save = fopen("file","w+");
         if(save == NULL){
             fprintf(stderr," \"file\" could not be opened!\n");
             return;
             }

   while(1){
      printf("Input:\n\n");
      printf("-n- Add new point\n");
      printf("-l- Output points\n");
      printf("-q- End program\n\n");
      printf("Your choice: ");
      scanf("%c", &choice);

      if(choice == 'q'){
            break;
        }

      switch(choice){
         case 'n' : input(save); break;
         case 'l' : output(save); break;
         default: printf("Unknown Input\n"); break;
      }
      fflush(stdin);
   }
   system("PAUSE");
   return 0;
}

Answer 1

你的函数output()中有三个错误。首先，您需要回放文件。其次，fread()读取的项目数必须为!=0或==1。第三，你在这个函数中而不是在程序结束时关闭了文件。

void output(FILE *save){
    fseek(save, 0, SEEK_SET);                          // added line
    while(fread(&point, sizeof(point), 1, save) != 0){ //corrected
        printf("x-coordinate: %f",point.x);
        printf("\ty-coordinate: %f",point.y);          // better layout
        printf("\tz-coordinate: %f",point.z);
        printf("\n\n");
    }
    //fclose(save);                                    // move to main()
}

此外，文件打开命令未使用您的#define，请从“文件”中删除引号。

save = fopen(file,"w+");                               // corrected

Answer 2

问题是您致电fread()。你把调用放在一个while循环中，直到它成功读取4个元素才会结束。您没有测试feof()。

尝试：

void output(FILE *save){
   while(1) {
       if (fread(&point, sizeof(point), 1, save) == 1) {
           printf("x-coordinatee: %f",point.x);
           printf("y-coordinate: %f",point.y);
           printf("z-coordinate: %f",point.z);
           printf("\n\n");
       }
       else
           break;
   }
   fclose(save);
}

file stream fread（） - 程序没有读取点

2 个答案: