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    Udf全局變量-外部變量External Variables,可在不同文件間共享

    2022-03-25  by:CAE仿真在線  來源:互聯網

    Udf全局變量-外部變量External Variables,可在不同文件間共享,如果要累計不同時間步的數據,就可以考慮這個方式。

    A.5.2. External Variables

    If you have a global variable that is declared in one source code file, but a function in another source file needs to use it, then it must be defined in the other source fi1e as an external variable. To do this, simp1y precede the variable declaration by the word extern as in

    extern real volume; 
    If there are several files referring to that variable then it is convenient to include the extern definition in a header (.h) file, and include the header file in all of the .c files that want to use the external variable. Only one .c file should have the declaration of the variable without the extern keyword. Below is an example that demonstrates the use of a header file.

    Important:   extern can be used only in compiled UDFs.

    A.5.2.1. Example
    Suppose that there is a global variable named volume that is declared in a C source file named file1.c

    #include "udf.h"
     real volume;  /* real variable named volume is declared globally */
     DEFINE_ADJUST(compute_volume, domain)
     /* code that computes volume of some zone */
     volume = ....
    If multiple sourc files want to use volume in the1r computations, then volume can be declared as an external variab1e in a header file (for example, extfile.h)

    /* extfile.h
     Header file that contains the external variable declaration for
     volume */
     extern real volume; /*聲明udf全局變量,這樣在h文件聲明就可以了*/
    Now another file named file2.c can declare volume as an external variable by simply including extfile.h.

    /* file2.c
     #include "udf.h"
     #include "extfile.h" /* header file containing extern declaration
           is included */
     /* code that computes the per unit volume source using the total
       volume computed in the compute_volume function from file1.c  */
     real tota1_source = ...;
     real source;
     source = total_source/volume;
     return source;


    但如果用static 靜態變量呢?這個不行




    The static operator has different effects depending on whether it is applied to local or global variables. When a local variable is declared as static the variable is prevented from being destroyed when a function returns from a call. In other words, the value of the variable is preserved. When a global variable is declared as static the variable is "file global." It can be used by any function within the source file in which it is declared, but is prevented from being used outside the file, even if is declared as external. Functions can also be declared as static. A static function is visible only to the source file in which it is defined.

    Important:   static variables and functions can be declared only in compiled UDF source files.

    A.5.3.1. Example - Static Global Variable
    /* mysource.c /*
     #include "udf.h"
     static real abs_coeff = 1.0; /* static global variable */
      /* used by both functions in this source file but is
       not visible to the outside */
     DEFINE_SOURCE(energy_source, c, t, dS, eqn)
       real source; /* local variable
       int P1 = ....; /* local variable
            value is not preserved when function returns */
       dS[eqn] = -16.* abs_coeff * SIGMA_SBC * pow(C_T(c,t),3.);
       source =-abs_coeff *(4.* SIGMA_SBC * pow(C_T(c,t),4.) - C_UDSI(c,t,P1));
       return source;
     DEFINE_SOURCE(p1_source, c, t, dS, eqn)
       real source;
       int P1 = ...;
       dS[eqn] = -abs_coeff;
       source = abs_coeff *(4.* SIGMA_SBC * pow(C_T(c,t),4.) - C_UDSI(c,t,P1));
       return source;


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