fgets() problem

[schwerzerspaner]

Hi!

I'm trying to write a program for my school project and I encountered a problem I can't resolve, nor understand.

I want to make a program that create a file and add records to this file until the user decide to stop.
Code:

#include <stdio.h>
#include <stdlib.h>
#include <iostream.h>
 
using namespace std;
 
typedef struct {
  char street[24];
  char city[20];
} Dest;
 
void add(char *filename)
{
  FILE *fp;
  Dest reg;
 
  fp=fopen(filename, "a"); 
 
  if(fp==NULL) perror("Error opening file");
  else
  {
    fseek(fp, 01, 2);
    fflush(stdin);
 
    printf("Street: ");
    fgets(reg.street, 24, stdin);
    printf("City: ");
    fgets(reg.city, 20, stdin);
 
    fwrite(&reg, sizeof(Dest), 1, fp);
    fclose(fp);
  }
};
 
int main()
{
  char test='d';
  char filename[25]="///root/test";
 
  while((test=='D')||(test=='d'))
  {
        system("clear");       
        add(filename);
 
        printf("\n To continue press D/d");
        cin >> test;
  };
 
  return 0;
}

The problem is: after a loop of while, if i continue to add record, the program don't let me enter record for "Street", jumps to next "City". The message "Street" appear on screen, but i can't enter data.

I use fedora and gnu c++.

Thanks for any tips.

P.S. Works on windows (DevC++) just fine, but in linux...

[Banfa]

    fflush(stdin);
 

You can not fflush stdin, it invokes undefined behaviour and you may get different program behaviour on different systems.

I suggest you start by removing this call.

[horace1]

in addtion to using fflush() on stdin (as indicated by banfa) you are mixing C and C++ I/O, i.e. using fgets() on stdin and cin >>, which can cause problems.

Your problem is probably being caused by

cin >> test;
 

where you will enter D (or some other character) followed by the newline key - the character is returned in variable test and the newline will be left in the input stream - the next fgets() will then return immediatly with an empty string (apart from newline character). Try replacing

cin >> test;
 

with

        test=getchar();  // read character
        getchar();       // read newline key
 

note that fgets() leaves the newline character \n on the end of the input string - you may not want this.

[schwerzerspaner]

Hi and thanks for replies.
I follow your advice, i modified the code: erase "fflush" and replace "cin" and now it's working.

Thanks a lot for your help and time.