Array of pointers - reading from a file - crashes

Question

Could you please point me to what am I doing wrong?

I am trying to write some code that will read data from a text file and save those data into an array of pointers, that point to to structs. It is critical that I don't use any global identifiers.

This is what I wrote but every time the function nactiProdukty (readProductsfromFile) ends it crasches with an error: First-chance exception at 0x73006500 in ConsoleApplication3.exe: 0xC0000005: Access violation executing location 0x73006500. But the reading from file seems to be working ok.

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

typedef struct produkt {
  char jmeno[20];
  int mnozstvi;
  int cena;
} tProdukt;


int SpoctiProdukty();
int Generuj(int min, int max);
void nactiProdukty(tProdukt **pole);


void main(){
  tProdukt **pole=NULL;

  int i;

  srand(time(NULL));
  nactiProdukty(pole);

  printf("test");
  scanf("%s");
}

int SpoctiProdukty(){
  FILE *data=fopen("data.txt","r");
  int count=0;
  while(fscanf(data,"%s %d") != EOF){
    count++;
  }
  fclose(data);
  return count;
}

int Generuj(int min, int max){
  return (rand()%(max-min)+min);
}

void nactiProdukty(tProdukt **pole){
  FILE *data=fopen("data.txt","r");
  int temp;
  int i;
  char temps[20];
  int pocet=SpoctiProdukty();
  //tProdukt **pole;

  pole=(tProdukt**)malloc(sizeof(tProdukt*)*pocet);
  for (i = 0; i < pocet; i++) {
    pole[i]=(tProdukt*)malloc(sizeof(tProdukt));
  }      

  for (i = 0; i < pocet; i++) {
    fscanf(data,"%s %d",temps,&temp);
    strcpy((*pole[i]).jmeno,temps);
    (*pole[i]).cena=temp;
    (*pole[i]).mnozstvi=Generuj(10,150);
  }
}

And don't include tags in your title. That's what the tags field is for. =) — J. Steen
– J. Steen, Commented Jan 11, 2013 at 12:59
@Alex What gave you the impression that this is C++? Though I agree that it isn't C# either. — Christian Rau
– Christian Rau, Commented Jan 11, 2013 at 13:01
I have repaired it, please observe the new formatting and emulate it in the future: sensible indentations, uniform indentations, all blocks indented, no needlessly large gaps in the code — Richard
– Richard, Commented Jan 11, 2013 at 13:31

simonc · Accepted Answer · 2013-01-11 13:23:35Z

1

The line

while(fscanf(data,"%s %d") != EOF){

is wrong. From the fscanf man page:

If the number of conversion specifications in format exceeds the number of pointer arguments, the results are undefined.

Crashing is a valid and common undefined result. You can fix this by providing variables for fscanf to write to, then ignoring the results:

int i;
char s[20];
while(fscanf(data,"%s %d", s, i) == 2){

answered Jan 11, 2013 at 13:23

simonc

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