Terminating a String

[JimJoyce]

I feel such a fool.
Up till a few years ago I used to be a C Instructor.
Now my C is very rusty.

If I strcpy part of a string into an empty buffer,
how do I place a '\0' at the end of the copied data?

 

[ArkM]

Don't worry: strcpy adds it. It's a part of the strcpy RTL function specification.

 

[JimJoyce]

I'm not so sure.
My output appears to be one long string.

I have a source-file (Dates of Easter, from a web site)

23 Apr 2000   20 Apr 2025   10 Apr 2050    7 Apr 2075
15 Apr 2001    5 Apr 2026    2 Apr 2051   19 Apr 2076
31 Mar 2002   28 Mar 2027   21 Apr 2052   11 Apr 2077
20 Apr 2003   16 Apr 2028    6 Apr 2053    3 Apr 2078
11 Apr 2004    1 Apr 2029   29 Mar 2054   23 Apr 2079
27 Mar 2005   21 Apr 2030   18 Apr 2055    7 Apr 2080
16 Apr 2006   13 Apr 2031    2 Apr 2056   30 Mar 2081
 8 Apr 2007   28 Mar 2032   22 Apr 2057   19 Apr 2082
23 Mar 2008   17 Apr 2033   14 Apr 2058    4 Apr 2083
12 Apr 2009    9 Apr 2034   30 Mar 2059   26 Mar 2084
 4 Apr 2010   25 Mar 2035   18 Apr 2060   15 Apr 2085
24 Apr 2011   13 Apr 2036   10 Apr 2061   31 Mar 2086
 8 Apr 2012    5 Apr 2037   26 Mar 2062   20 Apr 2087
31 Mar 2013   25 Apr 2038   15 Apr 2063   11 Apr 2088
20 Apr 2014   10 Apr 2039    6 Apr 2064    3 Apr 2089
 5 Apr 2015    1 Apr 2040   29 Mar 2065   16 Apr 2090
27 Mar 2016   21 Apr 2041   11 Apr 2066    8 Apr 2091
16 Apr 2017    6 Apr 2042    3 Apr 2067   30 Mar 2092
 1 Apr 2018   29 Mar 2043   22 Apr 2068   12 Apr 2093
21 Apr 2019   17 Apr 2044   14 Apr 2069    4 Apr 2094
12 Apr 2020    9 Apr 2045   30 Mar 2070   24 Apr 2095
 4 Apr 2021   25 Mar 2046   19 Apr 2071   15 Apr 2096
17 Apr 2022   14 Apr 2047   10 Apr 2072   31 Mar 2097
 9 Apr 2023    5 Apr 2048   26 Mar 2073   20 Apr 2098
31 Mar 2024   18 Apr 2049   15 Apr 2074   12 Apr 2099

I want to convert it into a 100 line file.

23 Apr 2000
15 Apr 2001
...
31 Mar 2024
20 Apr 2025
...
12 Apr 2099

I need to substring the 25 lines
and rearrange them as 100 lines
This is my code:

#include <stdio.h>

int main( )
   {
   FILE *fin, *fout;
   int  j, k, n;
   char buff[60];
   char yrs[25][4][12];
   char cent[100][12];
  
   fin  = fopen ( "east.txt", "r" );
   fout = fopen ( "e600.txt", "w" );

   for ( k=0 ; k<25 ; k++ )
      {
      fgets ( buff, 59, fin );
//puts ( buff );
      for ( n=0 ; n<4 ; n++ )
         {
         strncpy ( yrs[k][n], buff+n*12, 12 );
//puts ( yrs[k][n] );
         }
      }

   for ( n=0 ; n<4 ; n++ )
      {
      for ( k=0 ; k<25 ; k++ )
         {
      strcpy ( cent[n*25+k], yrs[k][n] );
//puts ( cent[n*25+k] );
         }
      }

   fputs ( buff, fout );
   for ( k=0 ; k<100 ; k++ )
      {
      fputs ( cent[k], fout );
//puts ( cent[k] );
      }

   fclose ( fin );
   fclose ( fout );
   }

The four //puts(), in column one, are purely trace code.

 

[Salem]

> char yrs[25][4][12];
> char cent[100][12];
Well both need to be 13 characters long to store the \0

> strncpy ( yrs[k][n], buff+n*12, 12 );
This doesn't copy a \0 by default. It's easy to do with
[tt]yrs[k][n][12] = '\0';[/tt]

>

   for ( n=0 ; n<4 ; n++ )
      {
      for ( k=0 ; k<25 ; k++ )
         {
      strcpy ( cent[n*25+k], yrs[k][n] );

If you swap the n and k loops around, you can just print directly from the yrs array.


--
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.

 

[JimJoyce]

Thanks, Salem.
That yrs[k][n][12] is the code I wanted.
I'd forgotten how to reference that nested array.

I'm not sure I need the arrays to be [13]
The strings are only 11 chars long.

I'll give them both a try.

 

[cpjust]

The strings are only 11 chars long.

Then why are you telling strncpy() to copy 12 characters instead of 11?

 

[JimJoyce]

Thanks cpjust,
As I said right at the beginning of the thread...
I feel such a fool !!!

Program's now working. It reads 600 years of easters,
which I'm analysing for frequencies and repetitions.

Many thanks to All you supporters,
JimJ