Controlling the memory area in C++

In C++, some objects may be constant and never modified. If your program is reentrant, having such objects exist in the code part is a storage and performance benefit.

As a programmer, you control where objects with global names and string literals exist. You can use the #pragma variable(objname, NORENT) directive to specify that the memory for an object with a global name is to be in the code area. You can use the ROCONST compiler option to specify that all const variables go into the code area.

In Figure 1, the variable RATES exists in the executable code area because #pragma variable(RATES,NORENT) has been specified. The variable totals exists in writable static area. All users have their own copies of the array totals, but the array RATES is shared among all users of the program.

Figure 1. Example of controllong the memory area

/*------------------------------------------------------------------*/
/* RATES is constant and in code area */
#pragma variable(RATES, NORENT)
const float RATES[5] = { 1.0, 1.5, 2.25, 3.375, 5.0625 };
float totals[5];
/*------------------------------------------------------------------*/

When you specify #pragma variable(objname,NORENT) for an object, and the program is to be reentrant, you must ensure that this object is never modified, even by constructors or destructors. Program exceptions or unpredictable behavior may result. Also, you must include #pragma variable(objname,NORENT) in every source file where the object is referenced or defined. Otherwise, the compiler will generate inconsistent addressing for the object, sometimes in the code area and sometimes in the writable static area.