c - char array on stack causes seg fault -

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• why writing string literal in c program segfault? 6 answers

this might expected i'm curious how/why happens.

when try use char * declared locally char * foo = "\xff\xff..." integer seg faults. if use malloc works when try access it. why happen?

#include <stdint.h> #include <stdio.h> #include <string.h> #include <inttypes.h> #include <stdlib.h>  int main(int argc, char **argv) {   unsigned char *buf = malloc(16);   memcpy(buf, "\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff\xff\xff\xff\xff\xff\xff", 16);   //unsigned char *buf = "\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff\xff\xff\xff\xff\xff\xff"; // seg faults if sue instead    uint64_t *k  = (uint64_t *) buf;   uint64_t *k2 = (uint64_t *) (buf + 8);   uint64_t  = 1000000000;    printf("-k =%" priu64 "\n", *k);   printf("-k2=%" priu64 "\n", *k2);    printf("iter * %" priu64  "\n", i);   (uint64_t c = 0; c < i; ++c)     {       *k  += 1;       *k2 -= 1;     }    printf("-k =%" priu64 "\n", *k);   printf("-k2=%" priu64 "\n", *k2);    return 0;  } 

output:

easytiger $ gcc -std=c99 tar.c -wall -o2 ; time ./a.out -k =0 -k2=18446744073709551615 iter * 1000000000 -k =1000000000 -k2=18446744072709551615 

string literals immutable. may not modify data stored there. ever.

even in c nowadays make clear , diagnosable lobbing const pointer type.

c++ requires it.