Page 384 - Programming Microcontrollers in C

Coding the Alpha Data 369

Read data from the keyboard
A function get() is used to read data from a keyboard into a
data buffer. This function is used in the monitor. A problem with
many such functions is that they do not provide proper protection
from a buffer overflow as the data are read in. The standard library
function fgets() almost meets the needs of this function and more.
The “more” in this case is the reason that we should not use the
fgets() in this case. This function is part of the standard library
and as such, it requires the definition of an input. The most often
used input file here is the one named stdin. When we construct
this system, we do not want to include all of the side effects of adding
the standard library to our system. Therefore, in this case, it is probably
best to write the function get() from scratch.
The function get() is shown below. This function takes two
parameters. The first is a pointer to a character string where the input
data are to be stored and the second is the length of this array. In the
event that the input data size exceeds the array size, the data array is
filled with zeros. Otherwise, the new line character is placed on the
end of the string and the string is terminated with a null character.

void get(char* a,int n)
{
/* read in field and terminate the read with an ‘\n’ */
int i=0,c;

while((c=getchar())!=’\n’ && i<(n-1))
a[i++]=c;
if(i<n-1)
{
a[i++]=’\n’;
a[i]=’\0';
}
else /* input did not terminate soon enough */
for(i=0;i<n;i++)
a[i]=0;
}
Listing 7-9: get() Input Data Routine