\'const int\' vs. \'int const\' in C and C: Are They Really the Same?

'const int' vs. 'int const' as Function Parameters in C and C

When declaring function parameters with const, it's crucial to distinguish between 'const int' and 'int const'. While they may seem identical, the order of the modifiers changes the interpretation of the declaration.

'const int' declares a variable that is constant (cannot be modified) and of type int. The emphasis here is on the const qualifier being applied to the variable.

'int const', on the other hand, declares a variable that is of type int and also constant. In this case, the const qualifier modifies the type, not the variable.

So, are these two functions identical?

<code class="c">int testfunc1 (const int a) { return a; }
int testfunc2 (int const a) { return a; }</code>

Yes, they are equivalent. Reading the declaration backwards clarifies this.

For 'const int':

• "a" is an integer that is "constant".

For 'int const':

• "a" is a "constant integer".

In both cases, "a" is both an integer and a constant.

However, the backward-reading trick becomes invaluable in complex declarations:

<code class="c">// "s" is a pointer to a char that is constant
const char *s;

// "t" is a constant pointer to a char
char *const t = &c;

// The char in "s" is constant, so you can't modify it
*s = 'A'; // Can't do

// The pointer in "s" is not constant, so you can modify it
s++; // Can do

// The char in "t" is not constant, so you can modify it
*t = 'A'; // Can do

// The pointer in "t" is constant, so you can't modify it
t++; // Can't do</code>

Remember, in C , const data members can be initialized either in the class declaration or in the constructor. Whereas in C, const data members are considered as symbolic constants and must be initialized in the declaration, which makes them very close to #define.

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