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const qualifier in structure

I want to know why the const qualifier in front of the array at the start of this program, supposedly makes the program more reliable and readable. I think it's because the specifiers in the printf statements have an easier time accessing the contents of an array if the array itself is constant. Is that correct?
#include <stdio.h> #define LEN 20 
const char * msgs[5] =
{ 
     "    Thank you,", 
     "You prove that a ",
     "is a special guy. We must meet over a "
     "at"  
     "and laugh"
}
 
struct names {
char first[LEN];
char last[LEN];
};
 
struct guy {
      struct names handle
       char favfood[LEN];
      char job[LEN] 
      float income;
};
 
int main(void)
{
struct guy fellow = {
      {"Thomas", "Villard"},
     "grilled salmon",
      "life coach",
      58112.00
};
 
 
 
     printf("Dear %s, \n\n", fellow.handle.first); 
     printf("%s%s.\n", msgs[0], fellow.handle.first);
     printf("%s%s\n", msgs[1], fellow.job);
     printf("%s\n", msgs[2]);
     printf("%s%s%s", msgs[3], fellow.favfood, msgs[4]);
     if (fellow.income > 150000.0) 
         puts("!!"); 
      else if (fellow.income > 75,000)
         puts("!");
      else
               puts(".");
      printf("See you soon.\n");
 
return 0;

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prebek
Asked:
prebek
1 Solution
 
mrjoltcolaCommented:
Nothing to do with printf().

const specifies that the data shall not be changed. It encourages against bad coding practices, because if the compiler is strict, it won't allow passing a const as a non-const argument, without the programmer explicitly casting.

It simply tells that the array is of pointers to strings char are essentially readonly. A "const" string or array cannot be assigned to without casting to hide the true type of pointer, and even then, could result in a code crash even if, due to attempt to write to read-only memory.

The difference is illustrated below. It is not the array itself that is const, it is an array of pointers TO const strings.
const char * msgs[2] = { "test", "test" };
 
int main() {
  msgs[0] = "ABC";   // legal, can point to a NEW const string
  msgs[0][1] = 'A';  // illegal, what msgs[0] points to is not writeable
}

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prebekAuthor Commented:
thanks, i get it now
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