Hi All,
I have a string represented by char* (I do not user string class):
char *s="abcd";
Assume I want to remove the last two elements of s. What is the
standard solution for this?
Can I just change the value of s[2] to '\0'?
Thanks a lot
Sara 9 1484 sa*******@gmail.com wrote:
Hi All,
I have a string represented by char* (I do not user string class):
char *s="abcd";
"abcd" is a string literal, it is a constant so you can't change it.
You can try, but the result is undefined.
If you want to manipulate strings, use std::string.
--
Ian Collins sa*******@gmail.com wrote:
Hi All,
I have a string represented by char* (I do not user string class):
char *s="abcd";
Assume I want to remove the last two elements of s. What is the
standard solution for this?
Using std::string.
Can I just change the value of s[2] to '\0'?
No.
The reason is a little involved. For starters, if you had
char const * s = "abcd"; // (*)
it would be obvious that you are trying to modify something declared const.
This is undefined behavior.
Second, you have
char * s = "abcd"
and that happens to be roughly equivalent to (*). The right hand side is
const and the conversion to something non-const is only allowed for
compatibility with C. The fact remains that you are trying to modify
the "abcd" string, which is const. That is still undefined behavior, see
[7.1.5.1/4] and [2.13.4/1] or just [2.13.4/2].
Best
Kai-Uwe Bux
On Oct 12, 2:41*pm, Kai-Uwe Bux <jkherci...@gmx.netwrote:
saraja...@gmail.com wrote:
Hi All,
I have a string represented by char* (I do not user string class):
char *s="abcd";
Assume I want to remove the last two elements of s. What is the
standard solution for this?
Using std::string.
Can I just change the value of s[2] to '\0'?
No.
The reason is a little involved. For starters, if you had
* char const * s = "abcd"; * * *// (*)
it would be obvious that you are trying to modify something declared const.
This is undefined behavior.
Second, you have
* char * s = "abcd"
and that happens to be roughly equivalent to (*). The right hand side is
const and the conversion to something non-const is only allowed for
compatibility with C. The fact remains that you are trying to modify
the "abcd" string, which is const. That is still undefined behavior, see
[7.1.5.1/4] and [2.13.4/1] or just [2.13.4/2].
Best
Kai-Uwe Bux
What if I use:
char s[4];
s[0]='a';
s[1]='b';
s[2]='c';
s[3]='d';
instead?
Is there any built-in method to erase a part of string defined as
char[] instead of std::string? sa*******@gmail.com wrote:
On Oct 12, 2:41*pm, Kai-Uwe Bux <jkherci...@gmx.netwrote:
>saraja...@gmail.com wrote:
Hi All,
I have a string represented by char* (I do not user string class):
char *s="abcd";
Assume I want to remove the last two elements of s. What is the
standard solution for this?
Using std::string.
Can I just change the value of s[2] to '\0'?
No.
The reason is a little involved. For starters, if you had
char const * s = "abcd"; * * *// (*)
it would be obvious that you are trying to modify something declared const. This is undefined behavior.
Second, you have
char * s = "abcd"
and that happens to be roughly equivalent to (*). The right hand side is const and the conversion to something non-const is only allowed for compatibility with C. The fact remains that you are trying to modify the "abcd" string, which is const. That is still undefined behavior, see [7.1.5.1/4] and [2.13.4/1] or just [2.13.4/2].
Best
Kai-Uwe Bux
What if I use:
char s[4];
s[0]='a';
s[1]='b';
s[2]='c';
s[3]='d';
instead?
Then you are not 0-terminated. Consequently, many function calls to standard
C-string functions will have undefined behavior.
Is there any built-in method to erase a part of string defined as
char[] instead of std::string?
Not that I would be aware of. But now you could do s[2] = \0. That, of
course, would not erase a block in the middle.
What is your reason not to use std::string?
Best
Kai-Uwe Bux
Kai-Uwe Bux wrote:
sa*******@gmail.com wrote:
[..]
>Is there any built-in method to erase a part of string defined as char[] instead of std::string?
Not that I would be aware of. But now you could do s[2] = \0. That, of
course, would not erase a block in the middle.
Nit-pick: now you could do
s[2] = 0
or
s[2] = '\0'
(You could of course put a backslash between the space and the zero, but
there has to be a line break immediately following the backslash <g>)
V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask
On Sun, 12 Oct 2008 14:22:01 -0700 (PDT), sa*******@gmail.com wrote:
>Hi All,
I have a string represented by char* (I do not user string class): char *s="abcd";
Assume I want to remove the last two elements of s. What is the standard solution for this?
This kind of string manipulation is more C than C++, but there is
still a library for working with these kinds of strings.
#include <cstring>
It's a bad idea to manipulate a string assigned from a literal,
though. That is...
char *s="abcd";
s[2] = 0; // Don't do this!
Instead, use...
char* s = new char [BUFFERSIZE];
std::strncpy (s, "abcd", BUFFERSIZE);
s [2] = 0;
In the above, I cut the string short by writing a new null terminator
to the appropriate character position.
However, this kind of stuff is very error prone, and tends to be a
cause of crashes, memory corruption, security issues and more. It's
very easy to end up reading/writing past the end of your buffers and
so on. Seriously, just use the std::string class - you'll regret it if
you don't.
On 2008-10-13 01:16, sa*******@gmail.com wrote:
On Oct 12, 2:41 pm, Kai-Uwe Bux <jkherci...@gmx.netwrote:
>saraja...@gmail.com wrote:
Hi All,
I have a string represented by char* (I do not user string class):
char *s="abcd";
Assume I want to remove the last two elements of s. What is the
standard solution for this?
Using std::string.
Can I just change the value of s[2] to '\0'?
No.
The reason is a little involved. For starters, if you had
char const * s = "abcd"; // (*)
it would be obvious that you are trying to modify something declared const. This is undefined behavior.
Second, you have
char * s = "abcd"
and that happens to be roughly equivalent to (*). The right hand side is const and the conversion to something non-const is only allowed for compatibility with C. The fact remains that you are trying to modify the "abcd" string, which is const. That is still undefined behavior, see [7.1.5.1/4] and [2.13.4/1] or just [2.13.4/2].
Best
Kai-Uwe Bux
What if I use:
char s[4];
s[0]='a';
s[1]='b';
s[2]='c';
s[3]='d';
instead?
If you must use char-arrays use
char s[] = "abcd";
this will ensure that the string is properly null-terminated.
Is there any built-in method to erase a part of string defined as
char[] instead of std::string?
Look up <cstringin your favourite C++ reference.
--
Erik Wikström
Stephen Horne wrote:
Instead, use...
char* s = new char [BUFFERSIZE];
std::strncpy (s, "abcd", BUFFERSIZE);
s [2] = 0;
Given this is almost *exactly* replicating what std::string would do
(except that it would do it more safely), I really can't understand why
you are giving this as a viable solution. Why not give the solution
using std::string rather than this? The end result will be the same, but
much safer and more didactic.
On Mon, 13 Oct 2008 16:34:33 GMT, Juha Nieminen
<no****@thanks.invalidwrote:
>Stephen Horne wrote:
>Instead, use...
char* s = new char [BUFFERSIZE]; std::strncpy (s, "abcd", BUFFERSIZE); s [2] = 0;
Given this is almost *exactly* replicating what std::string would do (except that it would do it more safely), I really can't understand why you are giving this as a viable solution. Why not give the solution using std::string rather than this? The end result will be the same, but much safer and more didactic.
Read the rest of the post.
In short, I *didn't* give it as a viable solution, I made it pretty
clear that it *wasn't* a sensible solution. But that doesn't mean that
I take an "I know this but you are not worthy" attitude.
Take a "do what I say" attitude and people will ignore you and do what
they want anyway. So provide the facts and explain why it's a bad
idea. That way, when they ignore you and do it anyway, they don't get
to blame your attitude when it all goes horribly wrong. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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