C & C++ string confusion

[Shawn O'Shea]

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> 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!)
>
>
> -Bruce
>
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