Am 08.11.15 um 08:45 schrieb Marko Rauhamaa:
Grant Edwards <invalid@invalid.invalid>:
On 2015-11-07, Marko Rauhamaa <ma...@pacujo.net> wrote:
"const" is a very ineffective tool that clutters the code and forces
you to sprinkle type casts around your code.
But it allows the compiler to warn you if you pass a pointer to a
read-only data to a function that expects a pointer to writable data.
Unfortunately, it doesn't:
========================================================================
#include <stdio.h>
#include <string.h>
int main()
{
const char name[] = "Tom";
char *p = strstr(name, "Tom");
strcpy(p, "Bob");
printf("name = %s\n", name);
return 0;
}
========================================================================
$ cc -o prog prog.c
$ ./prog
Bob
No warning.
That is strange. In C, I can see thet problem here, because it is
impossible to define a const correct strstr. But in C++ I have expected
that according to the overload, the const version of strstr would be
selected (http://www.cplusplus.com/reference/cstring/strstr/ ) . Still:
apfelkiste:Tests chris$ cat prog.cpp
#include <cstdio>
#include <cstring>
int main()
{
const char name[] = "Tom";
char *p = strstr(name, "Tom"); // this line should be an error
strcpy(p, "Bob");
printf("name = %s\n", name);
return 0;
}
apfelkiste:Tests chris$ g++ -Wall prog.cpp
apfelkiste:Tests chris$ ./a.out
Bus error: 10
It segfaults because on OSX, const can be stored in write-only memory.
apfelkiste:Tests chris$ g++ --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr
--with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin12.6.0
Thread model: posix
Christian
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