How to remove chars from a string pointer

[imLVcrazy]

Hi

Does any1 know of a method where you can search through a string and remove chars from a specific pointer until the new line. For example:

"This is a test @ A test this is"

how do make it so u search for a pointer (e.g.@) and make it this:

"This is a test"

Thanks for your help in advanced!!!

[JosAH]

Have a look at the strchr() function.

kind regards,

Jos

[imLVcrazy]

@JosAH
I know of dat function but, how do i delete the rest of the chars after using it is the problem. that will only point me to it, it wont delete or erase anything.

[JosAH]

@imLVcrazy
If that function return a non-NULL pointer set its value (i.e. to where it points) to '\0'; that effectively sets the end of the string; no need to erase anything at all.

kind regards,

Jos

[weaknessforcats]

The easiest way to remove chars from the middle of a string is to use strcpy() and copy the string into itself.

Suppose your string ro remove starts at address A and ends at address B. All you do is:

strcpy(A, B+1);

strcpy() will terminate using the \0 of the string.

Removing the end of a string is just a special case where B+1 is the \0 of the original string.

[donbock]

@imLVcrazy
Strictly speaking, you don't remove chars from a pointer, you remove them from a string pointed to by the pointer.

Not all strings can be modified, see examples below. The string pointed to by p1 is a string literal. Whether or not such a string can be modified is implementation-defined; and you should never rely on implementation-defined behavior. The const keyword in the declaration of pointer p2 prevents you from using p2 to modify the string it points at.

char *p1 = "foo";
 
char s[80] = "bar";
const char * p2 = s;

If the string cannot be modified then you need to make a second copy that you can modify.

[sridhard2406]

Hi
Please let me know, you want to remove the '@' character at every line , make it each line like below.

this is test1@ this is test1
this is test2 @this is test2
this is test3 @this is test3

After removing the '@' character
this is test1
this is test2
this is test3

[JosAH]

@weaknessforcats
Better don't do that; this is what the Standard has to say about overlapping areas:

The strcpy function copies the string pointed to by s2 (including
the terminating null character) into the array pointed to by s1 . If
copying takes place between objects that overlap, the behavior is
undefined.

memmove() is the only function that can handle overlapping areas.

kind regards,

Jos

[donbock]

@sridhard2406
So you want each string to end at the point where there is currently an '@' character. Suppose a newline appears somewhere after the '@" in the input string ... do you want the newline to appear in the output string? Suppose there isn't a newline at the end of the input string ... do you want to add a newline to the output string anyway?

Look back at response #4. It provides the simplest solution for you; with the following provisos:

• You need to do a little more if newlines are a special case;
• You need to operate on a copy of the input string if the input string cannot be modified.

[weaknessforcats]

Better don't do that; this is what the Standard has to say about overlapping areas:

Yes, but this is not an overlap situation. The original string memory allocation does not change. Only the characters are moved to the left. Works fine. Done it for years.

Doing anything other than moving characters to the left is the overlap case and that produces undefined results.

[JosAH]

@weaknessforcats
I think it is an overlapping problem: suppose you want to remove the character 'e' from the string "abcdefghij". You use a pointer to the character 'e' and a pointer to the character 'f' and do a strcpy(pe, pf); now suppose the strcpy() function starts copying from the end towards the beginning. You end up with the wrong string. (most (if not all) strcpy() implementations copy from the start to the ending '\0' character so there is no problem there).

kind regards,

Jos

[Banfa]

I have to agree with Jos on this. You may have done this overlapped copy for years but in all that time you have actually been relying on the specific implementation rather than on the standard defined behaviour.

It just happens that strcpy is a simple function and on the whole is implemented in the same way everywhere but that is not a requirement of the standard.

[donbock]

@sridhard2406
Is it necessary to support a method to escape the '@' character so there is a way for it to get into the output string? For instance,

Inputs:
This is a string: "foobar @ more stuff" @ text to be ignored
Special character \@ is important @ more text to be ignored
 
Outputs:
This is a string: "foobar @ more stuff" 
Special character \@ is important 

If so then your job is more complicated because you need to detect escaped '@' so that you can ignore it.

[JosAH]

@donbock
How about Occam's razor? I bet the OP hadn't even thought about your additional requirements yet ;-)

kind regards,

Jos

[donbock]

@JosAH
I went back and edited my post to emphasize that I'm supplying questions to help the OP clarify the requirements; not recommending what the answers to those questions should be. I want the OP to see the importance of thinking about the corner cases.

[JosAH]

@donbock
Which is AGT (A Good Thing (tm)); I'm just a lazy bastard: I give them what they asked for, no more no less ;-)

kind regards,

Jos

[imLVcrazy]

@sridhard2406
That is exactly what I'm looking for. To remove anything after ther @ symbol until a new line appears and then repeats the same thing on the new line.

[sridhard2406]

Hi,
If your data is in the file, read the all the information into buffer.and check how many bytes you have in your file (say For Example:Your file has the 1024 bytes).
Try to traverse the buffer until u reach the '@' character, if reached change the character as ' '(space) until u reach '\n' then traverse again until '@' ,
do same operation, until you reached all the bytes(1023).

let me know you got the logic.

[weaknessforcats]

now suppose the strcpy() function starts copying from the end towards

This contradicts K&R The ANSI C Programming Language Section 5.5 page 105.

I realize K&R is not the standard but by the same token, no C string library will implement a copy where you have to march the source string to the right just to copy to the left. That would be an implied strlen inside strcpy and that's not going to happen.

Also, remember that your pe and pf are addresses of char arrays and in C there is no way to tell the length of the target array (pe) so there is no way to copy into it from the right to the left.

I say again, this is not an overlap.

[JosAH]

@weaknessforcats
Ok have it your way then but your way contradicts the Standard. btw there is no need to tell the length of the target, i.e. if it is too short undefined behaviour occurs (a sigsegv will be raised usually).

kind regards,

Jos