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

186 Chapter5

HP C/iX Library Function Descriptions

fseek

fseek to do this:

…

int empno, bytes;

long total;

FILE *data;

struct emp empinfo;

/* check for usage error and open data file */

…

sscanf(argv[1], “%d”, &empno);

bytes = sizeof(empinfo);

total = (empno - 1) * bytes;

fseek(data, total, 0);

fread((char *)&empinfo, sizeof(empinfo), 1, data);

/* print out desired information */

…

exit(0);

}

In this program, argv[1] contains, using a command-line argument, the employee number

about whom information is desired. The employee number is converted to integer form

using sscanf. The number of bytes per employee structure is obtained using sizeof, and

is stored in bytes. The total number of bytes to skip in the data ﬁle is found by

multiplying the employee number (minus one) times the number of bytes per employee

structure. This is stored in total. Then, fseek() is used to seek past the speciﬁed

number of bytes, relative to the beginning of the data ﬁle. This leaves the next I/O

operation positioned at the start of the speciﬁed employee's information. The information

is read using fread().