[C,Linux/gcc] My strings manipulations seem crude

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October 25th, 2012, 11:17 PM

mathMajor

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[C,Linux/gcc] My strings manipulations seem crude

Is there a better way in C for me to accomplish the following string manipulations? It seems slightly convoluted.

Is there a way to use strings which might vary in length or am I forced to declare the size (as in strPr and fmtPr, below) ahead of time?

PHP Code:


		
			
#if defined(SUNDIALS_EXTENDED_PRECISION)

  char *fmt_spec = "L";

#elif defined(SUNDIALS_DOUBLE_PRECISION)

  char fmt_spec = 'l';

#else

  char fmt_spec = '';

#endif



char strPr[10] = "";

char fmtPr[10] = "";



sprintf( strPr, "%%4.0%sf", fmt_spec);

strcat( fmtPr, strPr);

strcat( fmtPr, "\t");

printf( fmtPr, t);



*fmtPr = '\0';

strcat( fmtPr, strPr);

strcat( fmtPr, "\n");

fprintf( t_steps, fmtPr, t);

Thanks for your feedback.

October 25th, 2012, 11:44 PM

salem

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I think I would go with

Code:

#if defined(SUNDIALS_EXTENDED_PRECISION)
  char *fmt_spec = "%4.0Lf";
#elif defined(SUNDIALS_DOUBLE_PRECISION)
  char *fmt_spec = "%4.0lf";
#else
  char *fmt_spec = "%4.0f";
#endif

printf( fmtPr, t); 
fputc('\t',stdout);

fprintf( t_steps, fmtPr, t);
fputc('\n',t_steps);

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October 26th, 2012, 12:38 AM

mathMajor

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Quote:

Originally Posted by salem

I think I would go with

Code:

#if defined(SUNDIALS_EXTENDED_PRECISION)
  char *fmt_spec = "%4.0Lf";
#elif defined(SUNDIALS_DOUBLE_PRECISION)
  char *fmt_spec = "%4.0lf";
#else
  char *fmt_spec = "%4.0f";
#endif

printf( fmtPr, t); 
fputc('\t',stdout);

fprintf( t_steps, fmtPr, t);
fputc('\n',t_steps);

Well, I don't want more than just the format specifier in the compiler code (by which I mean the #if..#endif) so I can use it with other lines to be printed. But I can definitely use the fputc to make the code better. I can just define the string once and I won't have to keep zeroing them out.

October 26th, 2012, 06:47 AM

OmegaZero

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These features may be of use to you:

Constant strings can be concatenated at compile-time.
Printf can take precision values from the argument list.

Code:

#include <stdio.h>
#define SHORT_FORMAT

#ifdef LONG_FORMAT
    #define MAKE_FORMAT(prec)  "%" prec "Lf"
#else
    #define MAKE_FORMAT(prec)  "%" prec "lf"
#endif

#ifdef LONG_FORMAT
    #define PREC_FORMAT  "%*.*Lf"
#else
    #define PREC_FORMAT  "%*.*lf"
#endif

int main() {
    float value = 1234.5678;

    printf( "The value is: " MAKE_FORMAT("4.0") "\n", value );
    printf( "The value is: " PREC_FORMAT "\n", 4, 0, value );

    return 0;
}

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[C,Linux/gcc] My strings manipulations seem crude

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