CODEWITHSUNDEEP
csegmentation-faultlinker-errorsheader-files
PCMasterRace007
PCMasterRace007

Reputation: 36

how to acess value of a extern variable within multiple header files

I have 2 header files, login.h and inmenu.h. login.h has included inmenu.h as well.

Now login.h defines an external variable extern char *password_login which is in a var.h header file as

printf("Enter the password: \n");
char *password_login = (char *)calloc(MAX, sizeof(char));
scanf("%1000s", password_login);

After that when i call inmenu() function from inmenu header file and try to access password_login value

char *tmpsqluppass = concatsqluppass(password_login, newpass);

This fails saying undefined reference to password_login

/usr/bin/ld: /tmp/ccKZpQvi.o: warning: relocation against password_login' in read-only section .text' /usr/bin/ld: /tmp/ccKZpQvi.o: in function inmenu': /home/legacy/Documents/project/src/../include/inmenu.h:27: undefined reference to password_login' /usr/bin/ld: warning: creating DT_TEXTREL in a PIE collect2: error: ld returned 1 exit status

This error goes away when i re-declare char *password_login in inmenu.h

But then segmentation fault occurs as the original value of password_login from login.h is lost and password_login points to 0x0 memory address and i use strcat() to concatenate password_login to another string.

How do i retain the value of password_login pointer in inmenu from login.

this is the concatsqluppass function

char *concatsqluppass(char *tmppass, char *tmppassnew)
{
    char *sql;
    sql = (char *)calloc(MAX, sizeof(char));
    strcat(sql, "update user_list set encpass = '");
    strcat(sql, tmppassnew);
    strcat(sql, "'");
    strcat(sql, " where encpass = '");
    strcat(sql, tmppass);
    strcat(sql, "'");
    strcat(sql, "\0");
    printf("query to be passed, \"%s\"", sql);
    return sql;
}

Upvotes: 0

Views: 581

Answers (2)

sudo pkill depression
sudo pkill depression

Reputation: 181

There’s a difference between declaring a variable and defining a variable. A variable can be declared at least once (but more is allowed). A variable can be defined once and only once. When you do extern int x you are declaring a variable. This says “this variable exists. I didn’t make it, someone else did. Just letting you know it exists“. When you do int x you are declaring and defining a variable. This says “I just made this variable. I created memory for it to live in. It exists. If you can see this statement you can use this variable”

If you put a definition (int x) in a header, chances are you’ll define a variable more than once, as multiple files will #include that file. This is why you should put the definition (int x) in the cpp file, as noone should #include a cpp. If other files need to also use the variable, a declaration (extern int x) can also go in the header file.

Doing this, you can put extern char *password_login in as many headers as you want and use the variable on those files.

Upvotes: 2

hsuecu
hsuecu

Reputation: 107

define password in login object file and define that same variable in imenu object file as

extern char * password_login
...
...
function(password_login,...);

make sure to use object file rather than writing code in header files.

Upvotes: 0

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