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Full Discussion: does any one know how to solve?
Top Forums Programming does any one know how to solve? Post 302228028 by redoubtable on Friday 22nd of August 2008 03:11:08 PM
Old 08-22-2008
Quote:
Originally Posted by shamrock
Imho that solution should be used for both static and dynamic cases. It's not advisable to create a 1000 element array on the stack and end up using only a small portion of it. Knowledge of sizeof operator is even more important if the code was accepting user input from the keyboard because in that scenario calls to malloc() printf() and fgets() have to be interleaved together in order to fill up a single empRec structure though its size should be known beforehand.
I agree with static cases when the total number of structs inside employee is known and sizeof() returns the whole size of the array so if we want to know the number of entries we just have to divide sizeof(employee) for sizeof(struct empRec). But in dynamic cases when the user wishes to add more entries in employee array struct, if the array (employee) is bigger (1000 structs) than the number of entries (struct empRec) it has, sizeof() will not help to determine the number of entries because it will give us the size of those 1000 structs and we just want to know those we're using. Also if pointers/malloc() are used, sizeof() won't be of any help I guess.
Code:
    static struct empRec employee[10] =
    {
        {"Peter North","4B-208",35400,{10,11,1983}},
        {"John Musa","2B-118",25400,{07,10,1993}},
        {"Paula Jeminova","1A-506",18700,{02,1,1990}},
        {"Patricia Silver","6C-123",52100,{14,21,2000}},
        {"Robert mill","4D-318",42100,{01,19,2008}}
    }

In this case, if we would want to add a few more entries dynamically we could not determine the number of existing entries (5) using sizeof(), because sizeof(employee) is the same as saying sizeof(struct empRec)*10.

This is why I was advising the original poster to use a NULL/empty struct reference as the final entry so the number of entries could be calculated by counting structs until an empty one was found.

I also agree that having 1000 entries is far too much, but I was not arguing about that. Anyway, how do you use sizeof() in dynamic cases?
 

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LEARN ABOUT REDHAT

strsyl

STRSYL(l)								 )								 STRSYL(l)

NAME

       STRSYL - solve the real Sylvester matrix equation

SYNOPSIS

       SUBROUTINE STRSYL( TRANA, TRANB, ISGN, M, N, A, LDA, B, LDB, C, LDC, SCALE, INFO )

	   CHARACTER	  TRANA, TRANB

	   INTEGER	  INFO, ISGN, LDA, LDB, LDC, M, N

	   REAL 	  SCALE

	   REAL 	  A( LDA, * ), B( LDB, * ), C( LDC, * )

PURPOSE

       STRSYL solves the real Sylvester matrix equation:
	  op(A)*X + X*op(B) = scale*C or
	  op(A)*X - X*op(B) = scale*C,

       where op(A) = A or A**T, and  A and B are both upper quasi- triangular. A is M-by-M and B is N-by-N; the right hand side C and the solution
       X are M-by-N; and scale is an output scale factor, set <= 1 to avoid overflow in X.

       A and B must be in Schur canonical form (as returned by SHSEQR), that is, block upper triangular with 1-by-1 and  2-by-2  diagonal  blocks;
       each 2-by-2 diagonal block has its diagonal elements equal and its off-diagonal elements of opposite sign.

ARGUMENTS

       TRANA   (input) CHARACTER*1
	       Specifies the option op(A):
	       = 'N': op(A) = A    (No transpose)
	       = 'T': op(A) = A**T (Transpose)
	       = 'C': op(A) = A**H (Conjugate transpose = Transpose)

       TRANB   (input) CHARACTER*1
	       Specifies the option op(B):
	       = 'N': op(B) = B    (No transpose)
	       = 'T': op(B) = B**T (Transpose)
	       = 'C': op(B) = B**H (Conjugate transpose = Transpose)

       ISGN    (input) INTEGER
	       Specifies the sign in the equation:
	       = +1: solve op(A)*X + X*op(B) = scale*C
	       = -1: solve op(A)*X - X*op(B) = scale*C

       M       (input) INTEGER
	       The order of the matrix A, and the number of rows in the matrices X and C. M >= 0.

       N       (input) INTEGER
	       The order of the matrix B, and the number of columns in the matrices X and C. N >= 0.

       A       (input) REAL array, dimension (LDA,M)
	       The upper quasi-triangular matrix A, in Schur canonical form.

       LDA     (input) INTEGER
	       The leading dimension of the array A. LDA >= max(1,M).

       B       (input) REAL array, dimension (LDB,N)
	       The upper quasi-triangular matrix B, in Schur canonical form.

       LDB     (input) INTEGER
	       The leading dimension of the array B. LDB >= max(1,N).

       C       (input/output) REAL array, dimension (LDC,N)
	       On entry, the M-by-N right hand side matrix C.  On exit, C is overwritten by the solution matrix X.

       LDC     (input) INTEGER
	       The leading dimension of the array C. LDC >= max(1,M)

       SCALE   (output) REAL
	       The scale factor, scale, set <= 1 to avoid overflow in X.

       INFO    (output) INTEGER
	       = 0: successful exit
	       < 0: if INFO = -i, the i-th argument had an illegal value
	       =  1: A and B have common or very close eigenvalues; perturbed values were used to solve the equation (but the matrices A and B are
	       unchanged).

LAPACK version 3.0						   15 June 2000 							 STRSYL(l)
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