HP C/iX Library Reference Manual (30026-90004)

Chapter 5 171

HP C/iX Library Function Descriptions

fread

}

This program reads the employee information contained in the binary ﬁle empdata. The

data in this ﬁle consists of concatenated streams of bytes describing each employee in a

400-employee company. The bytes are written such that, when read correctly, they

correspond exactly with the emp structure deﬁned in the program. The staff array is an

array of structures containing one structure for each employee.

In the fread() call, the sizeof(staff[0]) expression returns the number of bytes in the

emp structure. Because the same number of bytes are in each employee structure, any

element of the staff array can be speciﬁed as the sizeof argument; staff[0] is used in

this example. By counting the number of bytes in each structure member, you can

approximate the number of bytes returned by the sizeof operator (in this example, 40 +

40 + 8 + 6 + 2 + 4 = 100 bytes). This might vary due to padding performed by a

programming language or by machine architecture. Specifying EMPS as the

nitems

argument tells fread to read 400 structures. Thus, 100 x 400 = 40000 bytes are read,

ﬁlling in the information for the members of each structure contained in the staff array.

The fread() and fwrite() functions can read or write any type of data.

The following examples show some fread() calls that read different types of data:

To read a long integer:

long nint;

fread((void *)&nint, sizeof(nint), 1, stream);

To read an array of 100 long integers:

long nint[100];

fread((void *)nint, sizeof(nint[0]), 100, stream);

To read a double-precision ﬂoating-point value:

double fpoint;

fread((void *)&fpoint, sizeof(fpoint), 1, stream);

To read an array of 50 ﬂoating-point values:

float fpoint[50];

fread((void *)fpoint, sizeof(fpoint[0]), 50, stream);