Why does this function delete all the file data when I run it?

Question

When I run the program and I want to delete a product code then this function deletes all the file.

Could you please help me?

void PRODUCT_delete()
{
    int code;
    FILE *stock=fopen("stock.dat","wb+");

printf("PLEASE TYPE THE CODE OF THE PRODUCT YOU WISH TO DELETE:\t");

scanf(" %d",& code);
printf("\n");

fseek(stock,0,SEEK_END);

int fl_size=ftell(stock);
int quantity= fl_size/sizeof(product);

rewind(stock);

prdct cprd= (product *)malloc (sizeof(product)*quantity);
assert(cprd);

prdct cprd1= (product *) malloc(sizeof(product)*quantity);
assert(cprd1);

fread(cprd1,sizeof(product),quantity,stock);

int i;

for(i=0;i<quantity;i++)
    {
    if(cprd1[i].code!=code)
        {
    cprd[i]=cprd1[i++];

    }
        else
        {
            continue;
    }
     }

 fwrite(cprd,sizeof(product),quantity,stock);

 fclose(stock);
 free(cprd1);
 free(cprd);
 printf("\a THE PRODUCT DELETED!!!\n")
}

[Please don't cast the result of `malloc()`](http://stackoverflow.com/a/605858/3233393). — Quentin, Jan 28 '15 at 15:09

score 0 · Answer 1 · answered Jun 05 '14 at 15:13

0

See:

w+ truncate the file. You should use r+

Apparently the b modificator is for windows (non-posix systems).

answered Jun 05 '14 at 15:13

fjardon

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jarmod · Accepted Answer · 2015-01-28T15:05:19.493

0

A few problems:

opening a file with wb+ truncates the file, you should probably use a new file for output and then rename afterwards
<was wrong, deleted>
you need to decrement quantity if you remove the product code

edited Jan 28 '15 at 15:05

answered Jun 05 '14 at 15:20

jarmod

71,565
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1

1) I answered to use `r+` which is exactly what the OP wants, no need to use a new file. 2) You CAN copy structs, no need to use memcpy. – fjardon Jun 05 '14 at 18:01

Why does this function delete all the file data when I run it?

2 Answers2