Last update July 31, 2009

Faq Roadmap

(redirection from FAQ)

This page lists typical questions from D users. Most of them are simply recorded from the newsgroups without much reworking. There are of two other FAQs you might check:

Official FAQ D 1.x, D 2.x (Alpha) DocComments/FAQ
MKoD FAQ

This page is intended to act an simple authoring system to prepare content for both or any other FAQ someone might want to create. Once the questions receive a more formalized response, they will be moved to an appropriate FAQ location:

Table of contents of this page

Error Messages

What does a particular error message mean?

"Error: Access Violation" on printing a string

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Error Messages

What does a particular error message mean?

If it's a common error, it may already be on the Error Messages list.

"Error: Access Violation" on printing a string

You'll likely get an access violation if you try to print a char[] in this fashion:

printf("%s\n", input);

Use std.stdio.writef instead of printf, and std.stdio.writefln to print an extra newline after your output.

If you must use printf, this would be a correct way to do it:

printf("%.*s\n", input);

In D, arrays store their length, so character arrays need no terminating zero. In printf, the '%s' indicates a zero terminated string, so it fails when given a normal D string. The '%.*s' tells printf to expect a string preceded by its length. However, printf is still a C function, and so if the string contains embedded zero characters, printf will stop printing the string even before the specified length is reached. In other words, the '%.*s' will print until the length of the string is reached, or a zero is reached, whichever happens first.

The following examples will also work (though less efficient, because a temporary zero terminated string object is constructed):

printf(cast(char*) (input ~ "\n\0"));
printf(cast(char*) (input ~ \n ~ \0));
printf("%s\n",(char *)(input ~ \0));
printf("%s\n",(char *)input.dup);

Sometimes this is seen:

printf("%s\n",(char *)input);

but it is not always reliable, e.g. after:

char [] a="abcdefghij";
char [] input=a[3..4];
printf("%s\n",(char *)input);

it will not print "de" but "defghij" because no ending \0 is provided by the slice.

There is a HowTo/printf page giving more information on using printf.

Have another question?

The best way to get an answer to another question is to post it in one of the D newsgroups.