Output filename / Char* question.

This is a discussion on Output filename / Char* question. within the C Programming forums, part of the General Programming Boards category; Hello... I may have a fairly simple question, and if so I apologize. However, I haven't been able to discern ...

  1. #1
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    Output filename / Char* question.

    Hello... I may have a fairly simple question, and if so I apologize.
    However, I haven't been able to discern or find a solution, so here goes:

    I have a program which needs to create a set of files: "values.1","values.2","values.3"
    However, then number of such files cannot be hardcoded (as it is defined at runtime as the number of processors I chose to run on), and so the names of these files cannot be hardcoded into the source either.

    As such, I want to do the following (where the line I cannot do is sketched (but not correct)). The wrapping lines are included in case the context matters.


    Code:
    FILE *fout; /* Yes, I do usually do C++, but can't in this instance */
    int Np = 4;    /* this is the value that cannot be hardcoded */
    int i;
    char path[32] = "./values.";
    char filename[32];
    
      /* The FOR loop is not actually part of the code, but that's MPI specific,
          and if I can make it work in this case, I'm (1-eps) sure
          that I can make it work in the real code */
    
    for (i=0;i<Np;i++) {
       strcpy(filename,path);
       strcat(   filename,   (char *) i    );   /* THIS LINE SEEMS TO BE WRONG ... */
       fout = fopen(filename,"w");        /* THIS MAY WELL BE WRONG TOO... */
       fprintf(fout,"somestuff",somevalues);
       fclose(fout);
    
    }  /* endfor */

    When I try to run this, it compiles, but I do get a warning:
    PGC-W-0155-Pointer value created from a nonlong integral type (test.c: 112)

    And when I try to run it, I get the error:
    p0_20484: p4_error: interrupt SIGSEGV: 11



    Any help would be much appreciated on this problem, thank you in advance.

  2. #2
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    The simpler snprintf() can replace both strcpy() and strcat(), as in
    Code:
    snprintf(filename, sizeof filename, "%s%d", path, i);

  3. #3
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    Thanks... I hadn't known that.
    However, that is not the primary issue with the code...

    I need to know how to structure those couple lines so that I can open and write to the numbered files I want.

  4. #4
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    Nevermind, question answered....
    I missed something stupid... basically the difference between char a[] and char *a...

    thanks for the help

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