code: plan9front

ref: e72da62915b09d5673b0c0179ba8dfe045aeb8c3
dir: /sys/man/9/readnum/

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readnum, readstr \- device read routines
.ta \w'\fLint 'u
int readstr(ulong off, char *buf, ulong n, char *str)
int readnum(ulong off, char *buf, ulong n, ulong val, int size)
.I Readstr
.I readnum
simplify the return of strings and numbers from device
.I read
because they deal with any buffering and boundary cases.
Several parameters to the read call are often handed on directly
to these functions:
the file offset, as
.IR off ;
the address of the user's buffer, as
.IR buf ;
and the number of bytes requested, as
.IR n .
Both functions return the number of bytes they have stored in
.IR buf ,
and which can often be returned directly from the device read routine.
.I Readstr
satisfies a read by copying data into
.I buf
from the NUL-terminated string in
.IR str .
The data transferred is selected and limited by
.IR off ,
.I n
and the length of
.IR str .
.I Readnum
converts the unsigned integer
.I val
to a decimal representation in
.IR buf .
The value is right-justified in a field of
.IR size "-1"
places and is followed by a blank.
.I Size
can be the global constant
for 32-bit integers;
the largest
.I size
allowed is 64 bytes. 
.B /sys/src/9/port/devcons.c