How to create an excel file through a C program

[Andrew Poelstra]

In 100% standard C you can do it with

#include <stdio.h>
#include <stdlib.h>
int main(void)
{
FILE *ExcelFile = fopen("testdata.csv","w");
if (ExcelFile == NULL)
return -1;
fprintf(ExcelFile,"Column1,Column2,Column3\n1,2,3\n");
fclose(ExcelFile);
system("D:\\Program Files\\Microsoft Office\\Office\\excel.exe
testdata.csv");
return 0;
}

/Please/ quote you context.

And I love how you used the word "standard" and avoided entirely the
word "portable". The point of having standards is that you have a decent
level of portability.

 

[CBFalconer]

excel files are binary, and are most commonly used on platforms
where the distinction between binary and text is meaningful.
The OP would therefore be advised to use "wb" instead of "w".

The OP specified "excel file". What that consists of is not
specified in any C standard, so lacking specific other
specification, I stand by my solution. I think it was the Red
Queen that said "excel file means exactly what I intend it to
mean".

However it could well turn out that the "wb" is better suited.

--
"The power of the Executive to cast a man into prison without
formulating any charge known to the law, and particularly to
deny him the judgement of his peers, is in the highest degree
odious and is the foundation of all totalitarian government
whether Nazi or Communist." -- W. Churchill, Nov 21, 1943

 

[Flash Gordon]

The ShellExecute makes possible to ignore the path of the excel
executable. system() is not that clever, and the path is in this case
hardwired. The program is thus non-portable, but can be made to work in
any machine with Excel with very little effort

Actually, in Windows, there are commands you could have used that would
not have relied on knowing where excel is or even knowing what
application to use. However, how to do that is off topic here.

Of course, lcc-win32 offers the possibility of using the dispatch
interface of Excel and dynamically populating the cells, making excel
display a graphic of the data, whatever. But if I would have posted that
it would have been a 1500 line program full of windowish code... shudder.

Let's keep it at that. If the original posted is interested, we can
discuss that in the lcc group.

That is an appropriate redirect. Other Windows groups may have other
solutions available as well.

 

[Joe Wright]

fopen() the file with "wb" (write binary) mode, and
then fwrite() or fprintf() or putc() or fputc() whatever you need to.

You should probably avoid putw() and fputs(), though:
putw() works in terms of the type "int", which is not the same
size on all systems; and fputs() includes a terminating newline,
which is not the same character(s) on all systems.


What you need now is to know what the structure is of an excel file.
That's a topic beyond the scope of standard C, and is
subject to change without notice from Microsoft ("Documenting
a file structure hurts our ability to innovate!!") Inc.

You can find a long paper on the file format by googling for
excel file structure
for example, http://sc.openoffice.org/excelfileformat.pdf
has OpenOffice's documentation up to Excel 2003. You will likely
find the mass of information there rather daunting, and chances
are extremely high that if you were to attempt to implement the
full range yourself that you (or anyone) would make mistakes.
I would therefor suggest to you that you should either attempt to
find a pre-written Excel library (perhaps OpenOffice offers one),
or else that you take a big portability hit by confining yourself
to Windows and using one of Microsoft's development APIs.
Microsoft's APIs are discussed in microsoft-specific newsgroups.

fgets() will read a line including the trailing newline and terminate it
with '\0' as a string in memory.

fputs() will write the string including the newline, if it's there, and
not the terminating '\0'. Actually fputs() will write any string without
regard to newline.

 

[Joe Wright]

Zero opined:


Another possibility: use CSV format (comma separated values).

Yes, CSV is much easier to do in C but be warned that Excel does a poor
job of reading the .csv file. The Excel user generally has to reformat
various columns.

 

[Richard Bos]

That does not create an excel file: at most it creates a file that excel
is able to read.

And write, to a point.

There is another problem with the code that could arise especially
in Germany: comma might be the decimal delimeter (the equivilent
to the decimal point), and the field delimeter expected might be
the semi-colon. The 1,2 in the file might be interpreted as 1 + 2/10
(1.2) instead of as indicating the boundary between two cells.

Amazingly, Excel appears able to read real C(!)SV files even when
Windows is set to non-USAnian setting (at least, to Dutch ones); though
I have yet to find the option to make it write one.

At least CSV files can be written with proper C code, without having to
resort to MS-specific libraries. Normal Excel files can only be
approximated.

Richard

 

[Richard Bos]

Well, the requirements include an application that is basically only
available on one platform.

No, the requirements include writing a file for that application. This
can be done on a platform on which said application does not run itself.

In this case VB (or one of the embedded
VB-like thingies in Office) would be a decent choice.

It rarely if ever is.

Richard

 

[Richard G. Riley]

I need to create an excel file through a C program and then to populate
it.How can it be done?

What type of excel file? Excel supports many type formats for
import/export.

If it is the real "xls" file format then you need to familiarise
youeself with writing to and reading from binary files in C. Google will
show you how. Reading and writing binary files has its own issues over
doing it in normal ascii text mode : there can be platform specific
issues too.

Here is the excel file format explained : I can not comment on the
accuracy. There are many many complications to consider : byte ordering,
structure padding to name but 2.

http://sc.openoffice.org/excelfileformat.pdf

However, maybe you just need to write a text CSV file.

Good luck!