pointer passing segmentation fault
why when it is run gives:Code:#include <stdio.h> #include <time.h> char *tm2str(struct tm *timeInfo) { char *buf; sprintf (buf, "%d %d %d", timeInfo->tm_mday, timeInfo->tm_mon, (timeInfo->tm_year)+1900); return(buf); } int main () { time_t rawtime; struct tm * timeinfo; char *out; time ( &rawtime ); timeinfo = localtime ( &rawtime ); out = tm2str(timeinfo); printf("\n%s\n", out); return 0; }
Code:Segmentation fault (core dumped)
Well you didn't allocate any space for buf
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Thanks Salem for instant reply.
How to do that without affecting my objective?
If I change that declaration of buf i.e.
toCode:char *buf;
am getting the warning:Code:char buf[20];What could be the reason for thisCode:test.c: In function ‘tm2str’: test.c:9: warning: function returns address of local variable
Last edited by kapil1089thekin; 01-04-2011 at 11:57 AM.
Well, without knowing your objective, it is hard to say.
Try using malloc. Here is an example from the wiki for malloc. Pay attention to the "useful idiom" example as well. Also, don't forget to free your allocated memory when you are done with it.
You are allocating that space on the stack. When your function returns, the stack frame is gone, and so is your memory allocation. In other words, the data is trashed. Better to allocate some memory with malloc, and return the pointer to it.Originally Posted by kapil1089thekin
Last edited by kermit; 01-04-2011 at 11:59 AM.
kindly look into it!
which stack? Could you elaborate more? And when does something is stored in stack?
Give this a read.
I got that u are talking about stack frame?
then why this doesnt happens in other cases like when it is dealing with integers?
Because with integers, as per your example question, you are passing back a value which can be used immediately, or stored, or ignored. With an array, you are passing back a value as well, but that value is an address. By the time you get that adress, i.e., after the function returns, it is useless because the stack frame (where the address existed) has already been popped off.
Last edited by kermit; 01-04-2011 at 01:03 PM.
How aboutGet rid of the return.Code:void tm2str(struct tm *timeInfo, char *buf)
And in your main you call where you declared buf[20]:Code:tm2str(timeinfo, buf);
buf is a automatic variable for tm2str, when func is finished it is deallocated.am getting the warning:
Code:test.c: In function ‘tm2str’: test.c:9: warning: function returns address of local variable
instead of char *buf; put char *buf = malloc(20 * sizeof(char)); and in main after printf put free(out);.
Last edited by littletics; 01-04-2011 at 02:22 PM.
