Program mi bezi bez chyb, no pri ukoncovani, ked sa zavola funkcia free(retazec), sa stane "katastrofa".
*** glibc detected *** ./a.out: free(): invalid pointer: 0x00000000007f188f *** ======= Backtrace: ========= /lib/x86_64-linux-gnu/libc.so.6(+0x7e626)[0x7f2747e98626] ./a.out[0x402201] ./a.out[0x4009ef] ./a.out[0x400fe4] ./a.out[0x4010a2] ./a.out[0x400fdd] ./a.out[0x4009df] ./a.out[0x4009bd] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed)[0x7f2747e3b76d] ./a.out[0x4008f9] ======= Memory map: ======== 00400000-00403000 r-xp 00000000 08:01 29360399 a.out 00602000-00603000 r--p 00002000 08:01 29360399 a.out 00603000-00604000 rw-p 00003000 08:01 29360399 a.out 7f2747a00000-7f2747a15000 r-xp 00000000 08:01 24514046 /lib/x86_64-linux-gnu/libgcc_s.so.1 7f2747a15000-7f2747c14000 ---p 00015000 08:01 24514046 /lib/x86_64-linux-gnu/libgcc_s.so.1 7f2747c14000-7f2747c15000 r--p 00014000 08:01 24514046 /lib/x86_64-linux-gnu/libgcc_s.so.1 7f2747c15000-7f2747c16000 rw-p 00015000 08:01 24514046 /lib/x86_64-linux-gnu/libgcc_s.so.1 7f2747c16000-7f2747c18000 r-xp 00000000 08:01 24514038 /lib/x86_64-linux-gnu/libdl-2.15.so 7f2747c18000-7f2747e18000 ---p 00002000 08:01 24514038 /lib/x86_64-linux-gnu/libdl-2.15.so 7f2747e18000-7f2747e19000 r--p 00002000 08:01 24514038 /lib/x86_64-linux-gnu/libdl-2.15.so 7f2747e19000-7f2747e1a000 rw-p 00003000 08:01 24514038 /lib/x86_64-linux-gnu/libdl-2.15.so 7f2747e1a000-7f2747fcd000 r-xp 00000000 08:01 24514025 /lib/x86_64-linux-gnu/libc-2.15.so 7f2747fcd000-7f27481cc000 ---p 001b3000 08:01 24514025 /lib/x86_64-linux-gnu/libc-2.15.so 7f27481cc000-7f27481d0000 r--p 001b2000 08:01 24514025 /lib/x86_64-linux-gnu/libc-2.15.so 7f27481d0000-7f27481d2000 rw-p 001b6000 08:01 24514025 /lib/x86_64-linux-gnu/libc-2.15.so 7f27481d2000-7f27481d7000 rw-p 00000000 00:00 0 7f27481d7000-7f27481f9000 r-xp 00000000 08:01 24514122 /lib/x86_64-linux-gnu/libtinfo.so.5.9 7f27481f9000-7f27483f9000 ---p 00022000 08:01 24514122 /lib/x86_64-linux-gnu/libtinfo.so.5.9 7f27483f9000-7f27483fd000 r--p 00022000 08:01 24514122 /lib/x86_64-linux-gnu/libtinfo.so.5.9 7f27483fd000-7f27483fe000 rw-p 00026000 08:01 24514122 /lib/x86_64-linux-gnu/libtinfo.so.5.9 7f27483fe000-7f274841d000 r-xp 00000000 08:01 24514063 /lib/x86_64-linux-gnu/libncurses.so.5.9 7f274841d000-7f274861d000 ---p 0001f000 08:01 24514063 /lib/x86_64-linux-gnu/libncurses.so.5.9 7f274861d000-7f274861e000 r--p 0001f000 08:01 24514063 /lib/x86_64-linux-gnu/libncurses.so.5.9 7f274861e000-7f274861f000 rw-p 00020000 08:01 24514063 /lib/x86_64-linux-gnu/libncurses.so.5.9 7f274861f000-7f2748641000 r-xp 00000000 08:01 24514005 /lib/x86_64-linux-gnu/ld-2.15.so 7f2748825000-7f2748829000 rw-p 00000000 00:00 0 7f274883e000-7f2748841000 rw-p 00000000 00:00 0 7f2748841000-7f2748842000 r--p 00022000 08:01 24514005 /lib/x86_64-linux-gnu/ld-2.15.so 7f2748842000-7f2748844000 rw-p 00023000 08:01 24514005 /lib/x86_64-linux-gnu/ld-2.15.so 7fff93d58000-7fff93d79000 rw-p 00000000 00:00 0 [stack] 7fff93dff000-7fff93e00000 r-xp 00000000 00:00 0 [vdso] ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall] Aborted (core dumped)Nejak takto podobne to vyzera:
char * retazec_1 = "linuxos";
char * retazec;
int main()
{
funkcia1();
while(*retazec++ != '\0')
{
// ...........
}
funkcia2();
return 0;
}
void funkcia1()
{
retazec = (char *)malloc(sizeof(char)*sizeof(*retazec_1));
strcpy(retazec,retazec_1);
}
void funkcia2()
{
free(retazec );
}
do funkcia2() som dal
1) je to ekvivalent free() ?
2) ako uvolnit pamat funkciou free()?
2) Pamat sa uvolnuje, ak si ju skutocne alokujes (na halde). Je to komplementarna operacia k malloc()/calloc().
Teraz ti nevypise core dump, pretoze volanie free() na NULL nevykona ziadnu operaciu podla normy. Dostal si len po prstoch. ;)
* ano strlen(retazec) ↓
Tomuto velmi nerozumiem. Dealokujes ukazatel, ktory ukazuje niekam na koniec kopirovaneho "retazec_1".
Tomuto velmi nerozumiem.> Dealokujes ukazatel, ktory ukazuje niekam na koniec kopirovaneho "retazec_1".
Vsimni si, ze ukazatel retazec_1 menis - pri volani free() neukazuje na zaciatok miesta, ktore bolo pridelene pomocou malloc().
1) skor si myslel strlen(retazec_1)
2) Dealokujes ukazatel, ktory ukazuje niekam na koniec kopirovaneho "retazec_1".
potom:
je ok.
tym ten pointer menis.
char * retazec_1 = "linuxos"; char * retazec; char * retazec_zaloha; int main() { funkcia1(); while(*retazec++ != '\0') { // ........... } funkcia2(); return 0; } void funkcia1() { retazec = (char *)malloc(sizeof(char)*sizeof(*retazec_1)); strcpy(retazec,retazec_1); retazec_zaloha = retazec; } void funkcia2() { free(retazec_zaloha); }