problem with fprintf() output

Zach · Dec 5, 2010

I am trying to have fprintf() print the string:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

I tried:
fprintf(fpin,"<!DOCTYPE html PUBLIC "-"//W3C//DTD XHTML 1.1//EN\n");
fprintf(fpin,"
http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd>\n");

But this causes the following string to be displayed in my web
browser:
http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd>

I want it to be rendered not displayed. How can I fix the error in my
fprintf() statements?

Regards,
Zach

Ben Pfaff · Dec 5, 2010

Zach said:
I am trying to have fprintf() print the string:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

I tried:
fprintf(fpin,"<!DOCTYPE html PUBLIC "-"//W3C//DTD XHTML 1.1//EN\n");
fprintf(fpin,"
http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd>\n");

Use \" to output a literal ", e.g.:

fprintf(fpin,"<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.1//EN\"\n");
fprintf(fpin," \"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd\">\n");

Tim Harig · Dec 5, 2010

Use \" to output a literal ", e.g.:

fprintf(fpin,"<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.1//EN\"\n");
fprintf(fpin," \"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd\">\n");

Better yet, use some kind of template, in a config or resource file,
rather then generating boilerplate xhtml from inside of your C code.

Zach · Dec 5, 2010

Use \" to output a literal ", e.g.:

Excellent, just what I needed. Thanks!

Zach

Zach · Dec 5, 2010

Better yet, use some kind of template, in a config or resource file,
rather then generating boilerplate xhtml from inside of your C code.

Something to consider

Zach

Keith Thompson · Dec 6, 2010

Kenneth Brody said:
On 12/5/2010 1:25 AM, Zach wrote:
[...]

fprintf(fpin,"<!DOCTYPE html PUBLIC "-"//W3C//DTD XHTML 1.1//EN\n");
fprintf(fpin,"
http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd>\n");

Click to expand...

[...]

I see others have already answered, but you may be wondering why the code
you wrote didn't work, yet compiled.

Consider your "string":

"<!DOCTYPE html PUBLIC "-"//W3C//DTD XHTML 1.1//EN\n"

This is how C sees it:

A string literal: "<!DOCTYPE html PUBLIC "
A minus sign: -
Another string literal: "//W3C//DTD XHTML 1.1//EN\n"

So, your "string" is actually an integer representing the difference between
two "char*" values. (On my system, it's -24, though it could be virtually
anything.)

In fact, the behavior of the subtraction is undefined, since it
attempts to subtract pointers to two distinct objects. As always,
one possible result of undefined behavior is to quietly yield some
result which may or may not make sense.

Now, on my system, running your first fprintf line crashes the program, as
fprintf() is expecting a char*, not an integer, as the second parameter. (I
also get a warning about this at compile time.)

Again, passing a value of type ptrdiff_t (the signed integer type of the
result of subtracting two pointer values) to fprintf() with a format
that expects a char* argument results in undefined behavior. In this
particular case, the likely result is that the value -24 (if that's what
you happen to get) is interpreted as a char* value, possibly as
(char*)0xffffffe8 on a 32-bit system. Since there probably isn't
anything accessible at that address, a program crash is a very likely
result.

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problem with fprintf() output

Zach

Ben Pfaff

Tim Harig

Zach

Zach

Keith Thompson

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