strange outputs using fread

Hi all,

This is my first post on this site. I am taking c programming at college and plan on continuing with more advanced program classes.

I am writing a program that reads from a binary file (if one exists). If not the user can create and write data to one. On the next program run, fread will read from the file and populate an array before going to the fwrite functions. I put a bunch of printf's under the fread so I could test the results of the array. I also have some code commented out that I was toying with, trying to get this to work.

This is the output that I am getting from my printf tests

20
40
-858993460
60
-858993460
-858993460
80
-858993460
-858993460

I should be getting: 20,40,60,80,100,120,140,160,180,200

Here is my code, Is it the fread that is screwing things up? Or is it how the data is written (fwrite)? If it were a text file, I could at least eliminate one option.

Thanks in advance,

Michael

Code:

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void loadArray() {
    int userInput[MAXSIZE] = {0};
    int temp = 0;
    int count = 0;
    int counter=0;
    FILE *binaryPointer;
   
    binaryPointer = fopen("binaryFile.bin", "rb");
   
    if(binaryPointer) {
       
          while(!feof(binaryPointer)) {
                fread(&count, sizeof(int), 1, binaryPointer);
                userInput[counter] = count;
                counter++;
          }
          fclose(binaryPointer);
          printf("%d\n", userInput[0]);
          printf("%d\n", userInput[1]);
          printf("%d\n", userInput[2]);
          printf("%d\n", userInput[3]);
          printf("%d\n", userInput[4]);
          printf("%d\n", userInput[5]);
          printf("%d\n", userInput[6]);
          printf("%d\n", userInput[7]);
          printf("%d\n", userInput[8]);
          pause;
    }
    else {
          printf("The file does not exist, press any key to create one and write data to it\n");
          pause;
    }


    binaryPointer = fopen("binaryFile.bin", "ab+");   
            while (temp != -999){
                printf("Please enter a number to be stored in the array. Enter -999 to quit -  ");
                scanf("%d", &temp);
                userInput[counter] = temp;
                counter++;
                count++;
                fwrite(&temp, sizeof(int), count, binaryPointer);
            }
    fclose(binaryPointer);
           
}

---

Code:

---

fwrite(&temp, sizeof(int), count, binaryPointer);

---

shouldn't that be

Code:

---

fwrite(&temp, sizeof(int), 1, binaryPointer);

---

since you are writing one int each time through the loop. as it is, each time through the loop you write the value in temp plus whatever garbage is after temp in memory.

Code:

---

while(!feof(binaryPointer)) {

---

Read: Why it's bad to use feof() to control a loop

Quote:

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Originally Posted by dmh2000

Code:

---

fwrite(&temp, sizeof(int), count, binaryPointer);

---

shouldn't that be

Code:

---

fwrite(&temp, sizeof(int), 1, binaryPointer);

---

since you are writing one int each time through the loop. as it is, each time through the loop you write the value in temp plus whatever garbage is after temp in memory.

---

Thank you DMH, I should have tried that earlier. I do have a follow up question though.

I am getting the correct return now through my printf tests but the last number shows up twice in the array. For example, If I had 10 printf tests than I would get:

20
40
60
80
100
100
0
0
0
0

Any idea how I am getting the 2nd 100?

Thanks again

Quote:

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Originally Posted by generaltso78

Any idea how I am getting the 2nd 100?

Thanks again

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Read the post just above yours. Are you still using while (!feof(fp)) ? Get rid of that.

Thanks HK and c99. I wasn't thinking properly. Long day. Its all good now.