Reading from binary file in C

Question

I have the following struct:

struct Records
{
    int Number;
    char Name[20];
    float Salary;
};

Writing two records using:

fwrite(&MyRecords.Number, sizeof(&MyRecords.Number), 1, binaryfile);
fwrite(&MyRecords.Name, sizeof(&MyRecords.Name), 1, binaryfile);
fwrite(&MyRecords.Salary, sizeof(&MyRecords.Salary), 1, binaryfile);

After writing, Im having trouble reading from it.

FILE * read;
read = fopen("binaryfile.dat","rb");

for(int x =0;x<2;x++)
{
fread(&records.Number, sizeof(records.Number), 1, read);
fread(&records.Name, sizeof(records.Name), 1, read);
fread(&records.Salary, sizeof(records.Salary), 1, read);
printf("%d %s %f\n",records.Number,records.Name,records.Salary);
}

The first line gets printed twice, and the float comes out as some weird number. I've double and tripled checked for the past 2 hours yet I cant find out what im doing wrong :(

Can you show us how you open binaryfile and read files?

holgac
– holgac

2011-11-21 12:15:24 +00:00
Commented Nov 21, 2011 at 12:15 — holgac
– holgac, Commented Nov 21, 2011 at 12:15
Edited my post to add it

Amir
– Amir

2011-11-21 12:17:23 +00:00
Commented Nov 21, 2011 at 12:17 — Amir
– Amir, Commented Nov 21, 2011 at 12:17

Lindydancer · Accepted Answer · 2011-11-21 12:15:59Z

5

Hint:

sizeof(&foo)

Is not the same as:

sizeof(foo)

answered Nov 21, 2011 at 12:15

Lindydancer

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1 Comment

Lindydancer Over a year ago

It can be a number of things. 1) You haven't opened the file in binary mode (make sure "b" is specified for fopen). 2) Name might not have been null-terminated to start with (hint: create a print routine that you can call before writing the data to a file and after reading it back in, that way you could tell of the data was OK to start with).

halfer · Accepted Answer · 2020-01-14 08:49:33Z

3

You could write the whole struct in one go instead, makes it easier to read:

fwrite(&MyRecords, sizeof(MyRecords), 1, binaryfile);

besides that you also have wrong sizeof() it shouldn't be sizeof(&MyRec..) it should be sizeof(MyRec..) without &.

edited Jan 14, 2020 at 8:49

halfer

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answered Nov 21, 2011 at 12:18

AndersK

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1 Comment

Amir Over a year ago

Thanks, removing the & in the sizeof fixed the problem :)

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