I tried to print the line number of the current code by using:
#include <stdio.h>
void err (char *msg)
{
printf ("%s : %d" , msg , __LINE__);
}
int main ( int argc , char **argv )
{
ERR ("fail..");
return 0;
}
But i always get the wrong line number , it should be 10
instead of 5
, how can i fix this ?
Also i tried to use some macro:
#define ERR (msg) do { printf ("%s : %d\\n" , msg , __LINE__); } while (0)
and result in error: msg not declared
__LINE__
will give you the line on which it appears, which is always line 5.
To make this work, you will need to pass in __LINE__
as a separate parameter.
#include <stdio.h>
void err (char *msg, int line)
{
printf ("%s : %d" , msg , line);
}
int main ( int argc , char **argv )
{
err("fail..", __LINE__);
return 0;
}
An even better way to do this would be to define the invocation of such method as a macro , like so:
#define PRINTERR(msg) err((msg), __LINE__)
#define ERR(msg) printf("%s : %d", (msg), __LINE__)
Should do the trick.
You do not need the function!
__LINE__
gets the current line, meaning the line that it was called on. You need to pass it as a parameter:
ERR ("fail..", __LINE__);
Otherwise it will always be the line inside your error function, 5 in your example. Change your function to accept an int
type for the __LINE__
macro.
I would use the macro that @Ed Heal answered with. Also, the reason you are getting "msg not declared" is
that variables in macros need to be enclosed in parentheses (ie
because there is a space between the macro's name and the parenthesis that starts the parameter list. (msg)
).
您可以将ERR
宏:
#define ERR(msg) fprintf(stderr, "ERROR on line %d: %s\n", __LINE__, (msg))
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