C & C++ string confusion

[Jerry Feldman]

Just to add a bit more. The C++ versions of the standard C header files 
should be included:
For instance:
#include <cstdio>    NOT #include <stdio.h>
In all cases of header files defined by the C language standard prepend 
with a 'c' and drop the '.h'. But, this applies only to the standard C 
headers. The Unix/Linux standard header, unistd.h and other header files 
will still use the older syntax. The reason for this is that in some 
implementations, the C headers may not be C++ clean. Since I do mostly 
contract programming, I use the "when in Rome" philosophy, but it also 
applies to coding. When coding in C, code in C, when coding in C++ code 
in C++.

-- War story ---
Years ago when I worked in COBOL I was given a series of COBOL programs 
written by a FORTRAN programmer who hated COBOL. While I also knew 
FORTRAN and BASIC, this was one of the hardest programs I've had to 
debug, including the Tru64 kernel.
--- End of War story --

But, there are times when you need to use C language functions, and they 
don't know about std::string, iostream, or fstream. In my case I try to 
wrap these in their own classes, but the bottom line is that there is a 
task you are trying to accomplish, and it's always important to get it 
accomplished.

On 02/06/2009 01:54 PM, Shawn O'Shea wrote:
> I googled "open file c++" in Google and got this page:
> http://www.cplusplus.com/doc/tutorial/files.html
>
> There's an fstream include and you cin and cout to it like to do to 
> stdin/out.
>
> Also, no reason to call out to the shell. All standard file operations 
> (create/delete/copy/move/rename) are usually available natively in a 
> given language. This is true of C/C++. From the same site as above, 
> here's info on the C++ "remove" command:
> http://www.cplusplus.com/reference/clibrary/cstdio/remove.html
>
> -Shawn
>
> On Fri, Feb 6, 2009 at 1:23 PM, <bruce.labitt at autoliv.com 
> <mailto:bruce.labitt at autoliv.com>> wrote:
>
>     Maybe some on the list might know the answer to this...  I am
>     trying to
>     read n files, one at a time, and appending the data to a different
>     file.
>     Since the files are so large, I need to delete each of the n
>     files, once I
>     have captured the data.
>
>     Why on earth am I doing this?  My arrays are too large to fit in
>     memory
>     all at once (I used up all 32GB!!) so I have to process each row
>     of the
>     matrix separately.  (It slows stuff way down...)
>
>     I find string manipulation in C to be a bit arcane.  This is what
>     I have
>     come up with so far.  Unfortunately, (maybe fortunately?) the compiler
>     does not like my coding.  Oh yes, this has to be in a C or C++
>     dialect.
>     (No "I can do this in x lines of your favorite language" comments.
>     :) )
>
>     The code will be compiled using g++ on YDL to run on a QS22 (Cell
>     Processor) = Linux content :)
>
>     /start code snippet
>
>     main()
>     {
>      string filename;
>      string shelldelcmd;
>      string mydelstr;
>      char filenum[4];
>      char filenamec[20];
>      FILE * fidjj;
>
>      shelldelcmd.assign("rm -f ");
>
>      for (jj=0; jj<1000; jj++)
>      {
>      filename.assign("out");
>      sprintf(filenum, "%04d", jj); //generate string for file number, like
>     "0010"
>      filename.append(filenum);  // filename = "outxxxx", where xxxx = jj
>      filenamec = filename.c_str;           // <=====  COMPILER DIES HERE
>     ==========
>
>      fidjj = fopen(filenamec, "rb");       // <===== location of
>     second error
>      if (fidjj==NULL) {fputs ("File error, does not exist\n", stderr);
>     exit(1);}
>
>      fread some stuff...
>      fclose(fidjj);
>
>      mydelstr.assign(shelldelcmd);
>      mydelstr.append(filename);
>      mydelstr.append("\n");
>
>      cout << "my delete string is : " << mydelstr << endl;
>      system(mydelstr);     // delete the file I just read... !!!
>      fwrite data to a different file...
>      }
>     }
>
>     /end code snippet
>
>     Compiler error is: error; incompatible types of assignment of
>     '<unresolved
>     overloaded function type>' to 'char[20]'
>
>     If I just use the string "filename" instead of "filenamec" in
>     fopen I get
>     two errors, first the one in the previous paragraph, and second is:
>
>     error: cannot convert 'std::string' to const char * for argument
>     '1' to
>     'FILE * fopen(const char *, const char*)'
>
>     If you think I should step away from the keyboard, well, unfortunately
>     that is not an option.  I have to learn this stuff as I go
>     along...  And
>     no, I have never taken a class in C++.  I barely have the hang of C...
>     FWIW, I tried it in C and suffered some string craziness like
>     unexpected
>     overwriting.  It was ugly...  This approach seems cleaner, except
>     I do not
>     know how to convert the C++ strings to be able to use ordinary C
>     fopens...
>
>     Any tips or insight would be greatly appreciated...  (Awesome tips are
>     rewarded with beer!)
>


-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
PGP key id: 537C5846
PGP Key fingerprint: 3D1B 8377 A3C0 A5F2 ECBB  CA3B 4607 4319 537C 5846


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 251 bytes
Desc: OpenPGP digital signature
Url : http://mail.gnhlug.org/mailman/private/gnhlug-discuss/attachments/20090206/08a864a5/attachment-0001.bin