I am still suffering with pointers.
// main
// functon in other fileCode:int index = 50; char* flagx = mytable_get_flag(conn, index); printf("flag=%s\n", flagx);
I am getting warning: "return makes pointer from integer without a cast" at return retval in function.Code:char* mytable_get_flag(DBconn* conn, int index) { int retval = 0; // some code if (DBrows(result) > 0) retval = *DBgetvalue(result, 0, 0); return retval; }
How would I get my char* out to print value of this string in main?
You told the compiler you would be returning a char *, why are you trying to return an int?
Jim
What's DBgetvalue()'s return value? If it creates a string and returns it, then you should define retval as char * and then...
Code:... if (DBrows(result) > 0) retval = DBgetavlaue(result, 0, 0); return retval; }
Yes, yes, thank you.
I declared retval as int instead of char* (because of copying from other function).Code:char* retval = 0;
Now this work as expected.
No it is wrong. What is 0?
Is really dangerous. You should initialize with some valid adress not with an unknown address.... 0 is an unknown address I can't understand what you want to doCode:char * retval = 0 ;
Mr. Lnx, 0 is default value which will be returned if no data from database.
Should I set it to NULL insead, or what?
You are welcome
Also consider changing char *retval = 0; to char *retval = NULL; and check in the caller that the function has NOT returned NULL before attempting to print its returned string
0 is NULL in C++ but in C is most commonly defined as (void *)NULLOriginally Posted by Mr.Lnx
No it is wrong. What is 0?
Is really dangerous. You should initialize with some valid adress not with an unknown address.... 0 is an unknown address I can't understand what you want to doCode:char * retval = 0 ;
ah yes... sorry.
Interesting situation!
DBgetvalue(result, 0, 0); is actually a string (one char) but that string is number 1-4.
So if I set retval to "-1" then I haven't check if function return's null.
Instead I can check atoi() of returned char and if > 0 then something useful is returned.
Is this correct?
I think you mean: "NULL is often defined as 0 in C++, but in C it is most commonly defined as (void*)0". (Though I'm curious as to whether you really have proof of the latter claim.)
Look up a C++ Reference and learn How To Ask Questions The Smart Way
The Open Group Base Specifications Issue 7 - IEEE Std 1003.1, 2013 Edition
OpenBSD
FreeBSD
NetBSD
mingw
tinycc
Locally on my desktop PC:
lcc-win32: stdio.h
pelles-c: stdio.hCode:... /* Define NULL pointer value */ #ifndef NULL #define NULL ((void *)0) #endif ...
Visual C++ 2010: stddef.hCode:... /* macros */ #ifndef NULL #define NULL ((void *)0) #endif ...
Code:... /* Define NULL pointer value */ #ifndef NULL #ifdef __cplusplus #define NULL 0 #else #define NULL ((void *)0) #endif #endif ...
Last edited by migf1; 06-06-2013 at 09:12 PM.
Oh I forgot, my suggestion to OP for using NULL instead of 0 was just for readability reasons. The compiler is happy both ways.
But are you aware of any C++ implementation where NULL is defined to something different than plain 0? Just curious because you said "often".
Last edited by migf1; 06-06-2013 at 09:31 PM.
@laserlight:
Oh my, I just saw why you asked me that question in the 1st place!
I have a huge typo in my original post. I meant to write that in C NULL is most commonly defined as (void *)0 ( and not as (void *)NULL as I wrote there).
Btw, in C++ NULL is always defined as plain 0.
I'm really sorry about that!
Last edited by migf1; 06-07-2013 at 08:31 AM.
You're digging your hole deeper because, no, it's not.
A pointer with value zero and the NULL pointer will compare equal. That is not the same as NULL being defined as zero. In either C or C++.
As laserlight said, it is common in C++ for NULL to be defined as zero, and in C for it to be defined as (void *)0. But "is common" is not the same as "is always".
It is somewhat common practice in C++ to use a value of zero instead of the NULL macro. (That has changed, or is changing, with C++11, due to introduction of the nullptr keyword. I'll leave that note there, as this is a C forum, not a C++ forum).
You need to get your head around the notion that two distinct values can compare as equal, if there is a separate rule that specifies they are equal. The C standard has such a rule.
You might also want to look at this and this and this.
Last edited by grumpy; 06-07-2013 at 03:30 PM.
