Drawing lines

[Douglas Hay]

I want to draw a line chart with PHP. If I make my Draw() function the only
function call, it works fine. But if I display other data, and then call my
Draw() function, I get a bunch of graphics characters, and some text. The
text says I have already defined the header info. Here is the ledgible part
of the text

Warning: Cannot modify header information - headers already sent by (output
started at /home/virtual/site8/fst/var/www/html/laps/laps.php:10) in
/home/virtual/site8/fst/var/www/html/laps/lib.php on line 498

Here is my Draw() function. I just cut and pasted some code off a website.
I can't even draw a single line yet!

<?php
function Draw()
{
Header("Content-type: image/jpeg");
$image = ImageCreate(200,150);
$gray = ImageColorAllocate($image,204,204,204);
$blue = ImageColorAllocate($image,0,0,255);
ImageLine($image,10,10,150,30,$blue);
ImageJPEG($image);
ImageDestroy($image);
}?>

Any ideas why I cannot call the Header function here, or why my web page
just shows a bunch of text and graphic characters ?

Thanks,
Doug

[Stephen Oakes]

"Douglas Hay" <xx*@xxx.com> wrote...

Any ideas why I cannot call the Header function here

Make sure your <?php statement is the very start of the file. Any white
space will count as HTML output. Any HTML output sends the headers.

--
Stephen Oakes

[Erwin Moller]

Douglas Hay wrote:

I want to draw a line chart with PHP. If I make my Draw() function the
only
function call, it works fine. But if I display other data, and then call
my
Draw() function, I get a bunch of graphics characters, and some text. The
text says I have already defined the header info. Here is the ledgible
part of the text

Hi,

2 things I can think of:
1) Did you echo anything?
Like echo "myvar = $myvar";
This can also be caused by whitespaces before the script starts.

2) Maybe you made some error, and PHP spits it out.
So you are generating text (errormessages).

Tip:
View the result of the image in a texteditor, and look for errorlines.

Good luck.

Regards,
Erwin Moller

[Jerry Stuckle]

Douglas Hay wrote:

I want to draw a line chart with PHP. If I make my Draw() function the only
function call, it works fine. But if I display other data, and then call my
Draw() function, I get a bunch of graphics characters, and some text. The
text says I have already defined the header info. Here is the ledgible part
of the text

Warning: Cannot modify header information - headers already sent by (output
started at /home/virtual/site8/fst/var/www/html/laps/laps.php:10) in
/home/virtual/site8/fst/var/www/html/laps/lib.php on line 498

Here is my Draw() function. I just cut and pasted some code off a website.
I can't even draw a single line yet!

<?php
function Draw()
{
Header("Content-type: image/jpeg");
$image = ImageCreate(200,150);
$gray = ImageColorAllocate($image,204,204,204);
$blue = ImageColorAllocate($image,0,0,255);
ImageLine($image,10,10,150,30,$blue);
ImageJPEG($image);
ImageDestroy($image);
}?>

Any ideas why I cannot call the Header function here, or why my web page
just shows a bunch of text and graphic characters ?

Thanks,
Doug

Doug,

That's correct. Headers must be sent BEFORE anything else is sent.

You're example will create a page with a single jpeg. You can't have
any other content on the page.
--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
js*******@attglobal.net
==================

[Craig Storey]

Douglas Hay wrote:

I want to draw a line chart with PHP. If I make my Draw() function the only
function call, it works fine. But if I display other data, and then call my
Draw() function, I get a bunch of graphics characters, and some text. The
text says I have already defined the header info. Here is the ledgible part
of the text

Warning: Cannot modify header information - headers already sent by (output
started at /home/virtual/site8/fst/var/www/html/laps/laps.php:10) in
/home/virtual/site8/fst/var/www/html/laps/lib.php on line 498

Here is my Draw() function. I just cut and pasted some code off a website.
I can't even draw a single line yet!

<?php
function Draw()
{
Header("Content-type: image/jpeg");
$image = ImageCreate(200,150);
$gray = ImageColorAllocate($image,204,204,204);
$blue = ImageColorAllocate($image,0,0,255);
ImageLine($image,10,10,150,30,$blue);
ImageJPEG($image);
ImageDestroy($image);
}?>

Any ideas why I cannot call the Header function here, or why my web page
just shows a bunch of text and graphic characters ?

Thanks,
Doug

If you have used echoe/print etc.. then headers are already sent. To
get around this problem use two pages/php scripts. The first is the
display file containing your formatting page stuff. Somewhere in that
file you call the second script that creates the jpg, using <img
src="jpg-generating-php.php"> which is the script you alreay posted that
draws lines. This second script does set the headers, but they are
expected in the image tag.

Good luck.

[Douglas Hay]

Thanks for all the help, Craig's suggestion worked great and I got it
working now.

Thanks to all of you!

Doug

"Craig Storey" <cr*********@nrc.ca> wrote in message
news:d3**********@nrc-news.nrc.ca...

Douglas Hay wrote:

I want to draw a line chart with PHP. If I make my Draw() function the only function call, it works fine. But if I display other data, and then call my Draw() function, I get a bunch of graphics characters, and some text. The text says I have already defined the header info. Here is the ledgible part of the text

Warning: Cannot modify header information - headers already sent by (output started at /home/virtual/site8/fst/var/www/html/laps/laps.php:10) in
/home/virtual/site8/fst/var/www/html/laps/lib.php on line 498

Here is my Draw() function. I just cut and pasted some code off a website. I can't even draw a single line yet!

<?php
function Draw()
{
Header("Content-type: image/jpeg");
$image = ImageCreate(200,150);
$gray = ImageColorAllocate($image,204,204,204);
$blue = ImageColorAllocate($image,0,0,255);
ImageLine($image,10,10,150,30,$blue);
ImageJPEG($image);
ImageDestroy($image);
}?>

Any ideas why I cannot call the Header function here, or why my web page
just shows a bunch of text and graphic characters ?

Thanks,
Doug

If you have used echoe/print etc.. then headers are already sent. To
get around this problem use two pages/php scripts. The first is the
display file containing your formatting page stuff. Somewhere in that
file you call the second script that creates the jpg, using <img
src="jpg-generating-php.php"> which is the script you alreay posted that
draws lines. This second script does set the headers, but they are
expected in the image tag.

Good luck.