this isn't quite answered static const vs #define or #defining constants in c++.
in when did lot of programming in c, ansi c brand new. used #define define constants. i've been made aware no longer best practice (https://codereview.stackexchange.com/questions/123848/verifying-e-mail-address-in-c/123856#123856).
using #define can use previous constants define current constant, exampe is
#define email_char_array_size 40 #define good_email_address 1 #define bad_email_address 0 #define mimimum_user_name_length 1 #define at_sign_length 1 #define dot_length 1 #define minimum_domain_length 1 #define minimum_root_domain_length 2 #define miniumum_email_length mimimum_user_name_length + at_sign_length + minimum_domain_length + minimum_root_domain_length i have program (below) have attempted use static const rather #define, constant miniumum_email_length doesn't compile when try use static const using previous constants. there way use defined constants in static const type declaration?
const_testemail.c:12:5: error: initializer element not constant static const int miniumum_email_length = (mimimum_user_name_length + at_sign_length + minimum_domain_length + minimum_root_domain_length); #include <stdio.h> #include <string.h> static const int email_char_array_size = 40; static const int good_email_address = 1; static const int bad_email_address = 0; static const int mimimum_user_name_length = 1; static const int at_sign_length = 1; static const int dot_length = 1; static const int minimum_domain_length = 1; static const int minimum_root_domain_length = 2; /* doesn't compile * static const int miniumum_email_length = mimimum_user_name_length + at_sign_length + minimum_domain_length + minimum_root_domain_length; * */ #define miniumum_email_length (mimimum_user_name_length + at_sign_length + minimum_domain_length + minimum_root_domain_length) int isemailaddressproper(const char emailaddress[email_char_array_size]) { int emailaddressisgood = good_email_address; int lengthofemailaddress; char *atsignlocation, *pos2; int rootdomainlength; lengthofemailaddress = strlen(emailaddress); if (lengthofemailaddress < miniumum_email_length) { printf("the length of email address less minimum lenght %d\n", miniumum_email_length); emailaddressisgood = bad_email_address; } atsignlocation = strchr(emailaddress, '@'); /* first instance of @ */ if (!atsignlocation) { printf("there no @ in email address\n"); emailaddressisgood = bad_email_address; return emailaddressisgood; } if (atsignlocation == emailaddress) { /* @ first character? */ printf("there no user name in email address, @ first character\n"); emailaddressisgood = bad_email_address; } pos2 = strrchr(emailaddress, '@'); /* find other @ */ if ((pos2) && (atsignlocation != pos2)) { printf("there more 1 @ in email address\n"); emailaddressisgood = bad_email_address; } pos2 = strrchr(emailaddress, '.'); /* last instance of '.' */ if (atsignlocation > pos2) /* . before @ ? */ { printf("there no root domain in email address\n"); emailaddressisgood = bad_email_address; } pos2++; rootdomainlength = lengthofemailaddress - ((int)(pos2 - emailaddress)); /* if root domain less length 2 */ if (rootdomainlength < minimum_root_domain_length) { printf("the root domain length (%d) less minimum length required (%d) in email address\n", rootdomainlength, minimum_root_domain_length); emailaddressisgood = bad_email_address; } return emailaddressisgood; } void getandvalidateemailaddress(char emailaddress[email_char_array_size]) { int emailaddressisgood = bad_email_address; char tempemail[email_char_array_size]; while (!emailaddressisgood) { scanf("%39s", tempemail); emailaddressisgood = isemailaddressproper(tempemail); if (!emailaddressisgood) { printf("the email address not in proper format, please re-enter email address\n"); } } strcpy(emailaddress, tempemail); } main() { char emailaddress[email_char_array_size]; printf("please enter email address\n"); getandvalidateemailaddress(emailaddress); printf("the email address entered %s\n", emailaddress); }
c not have symbolic constants other enum-constants (which of type int). #define macro , part of preprocessor. textual replacement before actual c language compilation.
const qualified variables semantically still variables. qualifier guarantee programmer not change value. compiler may rely on guarantee. breaking contract invokes undefined behaviour, not enforced run-time environment.
static initialisers , array indexes @ file-level require constant expression, error. briefly, constant expression must yield constant value @ compile-time, cannot use variables.
note array parameter in function has similar problem. here can use variable length array. however, either can use empty length ([]) or pass length preceeding parameter explicitly; global variables don't work:
int isemailaddressproper(size_t len, const char emailaddress[len]) c++ different language similar syntax/grammar, , quite different semantics same grammar. cannot apply knowledge on language other.
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