Hi ,
I have a problem with strcat...
The code is:
This is not working and giving segmentation fault.Code:char *str="/home/bargi/"; strcat(str,"temp.txt");
Can anybody suggest me the correct way of doing it and also the mistake I am making
Thanks
Hi ,
I have a problem with strcat...
The code is:
This is not working and giving segmentation fault.Code:char *str="/home/bargi/"; strcat(str,"temp.txt");
Can anybody suggest me the correct way of doing it and also the mistake I am making
Thanks
That's because the string literal that str points at is a constant value - it can not be modified. Nor is there any space to store the extra string that you are concatenating onto it, but that's not why it's crashing.
You need to make it an initialized char array, and make sure it's big enough to hold the full string.
char * variables that are initialized to a string shoudl really be declared "const char *" - that way, the compiler will tell you when you are doing silly things like trying to write to the string that should not be modified.
--
Mats
Compilers can produce warnings - make the compiler programmers happy: Use them!
Please don't PM me for help - and no, I don't do help over instant messengers.
The problem is that str is a pointer that points to the first char of a string literal. Attempts to modify the string literal results in undefined behaviour, and a segmentation fault is one example of that. Rather, you need to make sure that str points to the first char of a char array whose contents can be modified, and that there are enough chars in the char array to accomodate the result of strcat, including the null terminator, e.g.,
Code:char str[21] = "/home/bargi/"; strcat(str, "temp.txt");
Look up a C++ Reference and learn How To Ask Questions The Smart WayOriginally Posted by Bjarne Stroustrup (2000-10-14)
Thanks for help....
It mean that I have to declare the size of str....
But it printing something this:char str[] = "/home/bargi/";
strcat(str, "temp.txt");
Can you explain me the reason....??*** stack smashing detected ***: ./str terminated
======= Backtrace: =========
/lib/tls/i686/cmov/libc.so.6(__fortify_fail+0x48)[0xb7e35138]
/lib/tls/i686/cmov/libc.so.6(__fortify_fail+0x0)[0xb7e350f0]
./str(__gxx_personality_v0+0x11e)[0x804859a]
/lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe0)[0xb7d5e450]
./str(__gxx_personality_v0+0x35)[0x80484b1]
======= Memory map: ========
08048000-08049000 r-xp 00000000 08:05 2064596 /home/bhagwat/malloc/str
08049000-0804a000 rw-p 00000000 08:05 2064596 /home/bhagwat/malloc/str
0804a000-0806b000 rw-p 0804a000 00:00 0 [heap]
b7d47000-b7d48000 rw-p b7d47000 00:00 0
b7d48000-b7e91000 r-xp 00000000 08:05 3899630 /lib/tls/i686/cmov/libc-2.7.so
b7e91000-b7e92000 r--p 00149000 08:05 3899630 /lib/tls/i686/cmov/libc-2.7.so
b7e92000-b7e94000 rw-p 0014a000 08:05 3899630 /lib/tls/i686/cmov/libc-2.7.so
b7e94000-b7e97000 rw-p b7e94000 00:00 0
b7e97000-b7ea1000 r-xp 00000000 08:05 3850252 /lib/libgcc_s.so.1
b7ea1000-b7ea2000 rw-p 0000a000 08:05 3850252 /lib/libgcc_s.so.1
b7ea2000-b7ea3000 rw-p b7ea2000 00:00 0
b7ea3000-b7ec6000 r-xp 00000000 08:05 3899639 /lib/tls/i686/cmov/libm-2.7.so
b7ec6000-b7ec8000 rw-p 00023000 08:05 3899639 /lib/tls/i686/cmov/libm-2.7.so
b7ec8000-b7fb0000 r-xp 00000000 08:05 5226835 /usr/lib/libstdc++.so.6.0.9
b7fb0000-b7fb3000 r--p 000e8000 08:05 5226835 /usr/lib/libstdc++.so.6.0.9
b7fb3000-b7fb5000 rw-p 000eb000 08:05 5226835 /usr/lib/libstdc++.so.6.0.9
b7fb5000-b7fbb000 rw-p b7fb5000 00:00 0
b7fc9000-b7fcc000 rw-p b7fc9000 00:00 0
b7fcc000-b7fcd000 r-xp b7fcc000 00:00 0 [vdso]
b7fcd000-b7fe7000 r-xp 00000000 08:05 3850309 /lib/ld-2.7.so
b7fe7000-b7fe9000 rw-p 00019000 08:05 3850309 /lib/ld-2.7.so
bf8a4000-bf8b9000 rw-p bffeb000 00:00 0 [stack]
bargiAAAAAborted
Also is this rule apply for strcpy() function and what are the best ways to implement them...
I will be thank ful to you
Thanks
Yes, if you initialise str that way (without explicitly stating the size of the char array) it will have only enough space for the original string. You would not be able to correctly concatenate anything.
Look up a C++ Reference and learn How To Ask Questions The Smart Way
strcat(str, "temp.txt");
Now you are adding 8 more bytes to str, which is already ONLY 13 bytes. You need to start with a bigger str:
Code:char str[32]="/home/bargi";
C programming resources:
GNU C Function and Macro Index -- glibc reference manual
The C Book -- nice online learner guide
Current ISO draft standard
CCAN -- new CPAN like open source library repository
3 (different) GNU debugger tutorials: #1 -- #2 -- #3
cpwiki -- our wiki on sourceforge
thanks laser for your help.......
I want some help from regarding C programming....
Actually I have just started working on C specific project and there are lots of pointer memory intialization in this....
Can you suggest me the best ways in initialization of memory and ways to handle and debug memory faults....as I am new to C programming...
Thanks for your help...
Regards
Bargi
A great way to "get comfortable" with pointers and memory management is to do a simple linked list exercise using a tutorial (find one you like); just write a basic linked list program where you can add and remove nodes, and print the list properly to the screen.
By the time you're done, you'll have a bunch more experience with malloc() and free() and using pointers to access blocks of data in memory.
C programming resources:
GNU C Function and Macro Index -- glibc reference manual
The C Book -- nice online learner guide
Current ISO draft standard
CCAN -- new CPAN like open source library repository
3 (different) GNU debugger tutorials: #1 -- #2 -- #3
cpwiki -- our wiki on sourceforge
