strtol() and zero

[Marlene Stebbins]

Suppose I'm using strtol() to convert a command line string
to a number and I want to check that the input to strtol() is
not non-numeric. strtol() returns zero if input is non-numeric,
so I can write something like this:

if((x = strtol(argv[1], NULL, 10))==0)
exit(EXIT_FAILURE);

That catches non-numeric input alright, but zero is a perfectly
good number that might be input to my program. How can I use
strtol() to convert zero while checking for non-numeric input?

[Joe Wright]

Marlene Stebbins wrote:

Suppose I'm using strtol() to convert a command line string
to a number and I want to check that the input to strtol() is
not non-numeric. strtol() returns zero if input is non-numeric,
so I can write something like this:

if((x = strtol(argv[1], NULL, 10))==0)
exit(EXIT_FAILURE);

That catches non-numeric input alright, but zero is a perfectly
good number that might be input to my program. How can I use
strtol() to convert zero while checking for non-numeric input?

Assume this prototype..

long strtol(const char *s, char **endp, int base);

Rather than passing NULL as the second argument, pass the address of
a local char* like this..

long x;
char *end;
x = strtol(argv[1], &end, 10);
if (argv[1] == end) exit(EXIT_FAILURE);

--
Joe Wright mailto:jo********@comcast.net
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Jack Klein]

On Tue, 14 Dec 2004 21:47:31 GMT, Marlene Stebbins <ma*****@mail.com>
wrote in comp.lang.c:

Suppose I'm using strtol() to convert a command line string
to a number and I want to check that the input to strtol() is
not non-numeric. strtol() returns zero if input is non-numeric,
so I can write something like this:

if((x = strtol(argv[1], NULL, 10))==0)
exit(EXIT_FAILURE);

That catches non-numeric input alright, but zero is a perfectly
good number that might be input to my program. How can I use
strtol() to convert zero while checking for non-numeric input?

Explanation and illustration:

http://jk-technology.com/c/code/strtol.html

--
Jack Klein
Home: http://JK-Technology.Com
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