This gives seg fault. Why? Thanks.Code:#include <stdio.h> #include <stdlib.h> #include <string.h> typedef struct { int value; char* value2; } demo; void test(int* v) { *v=1; } void test2(char* v) { strcpy(v, "ape"); } int main() { demo* d; d=(demo*)malloc(sizeof(demo)); test(&(d->value)); printf("%d", d->value); // Initialize value2 first d->value2=(char*)(10*sizeof(char)); test2(d->value2); puts(d->value2); }
Perhaps because you forgot to call malloc ?
Your address is 10, not a pointer to 10 bytes.Code:$ gcc -W -Wall -Wextra -g bar.c $ gdb ./a.out GNU gdb (GDB) 7.1-ubuntu Copyright (C) 2010 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". For bug reporting instructions, please see: <http://www.gnu.org/software/gdb/bugs/>... Reading symbols from /home/sc/Documents/coding/a.out...done. (gdb) run Starting program: /home/sc/Documents/coding/a.out Program received signal SIGSEGV, Segmentation fault. memcpy () at ../sysdeps/x86_64/memcpy.S:91 91 ../sysdeps/x86_64/memcpy.S: No such file or directory. in ../sysdeps/x86_64/memcpy.S (gdb) where #0 memcpy () at ../sysdeps/x86_64/memcpy.S:91 #1 0x000000000040063d in test2 (v=0xa <Address 0xa out of bounds>) at bar.c:15 #2 0x0000000000400697 in main () at bar.c:27
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.
oh yeah i forgot to put malloc in line 26
Well it's another fantastic example of why you shouldn't cast malloc in a C program!
FAQ > Casting malloc - Cprogramming.com
Had you not beaten the compiler into submission with the cast, you would have gotten a warning from the compiler.
Instead, the OS just killed your program with no information.
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.
