Help with String Operations

[pgcrooks]

Hey all,

I've searched far and wide for an answer to this but have yet to find a case which is the same as mine...

Basically I have a string (indata), eg "1234" and I want to be able to copy the "23" from this and store it in a seperate string (oldadd). I have tried strcpy but it only seems to want to copy the entire string, not just the single element which I want.

Originally I had the following (left out declarations since I'm being lazy here):

indata = "1234";
strncpy(oldadd, indata[1], 1);
strncat(oldadd, indata[2], 1);

With the intention of copying the 2nd char of the string indata to oldadd and then sticking the 3rd char onto the end of oldadd later. This is the only way I can think of doing it, I can't use a strstr or strchr because the little bit I want will always be different however I know that it will always be the 2nd and 3rd character of the indata string.

Thanks for any help, I hope this hasn't been answered somewhere else which I've missed :S

pgcrooks

[anon]

Have you tried to use strncpy in a proper way (call once to copy two characters)?

[pgcrooks]

Have you tried to use strncpy in a proper way (call once to copy two characters)?

Hey anon, thanks for the quick reply.

The problem with strcpy or strncpy is that it copies the string from the start, I want to ignore the 1st character (ie. start at indata[1] and not indata[0]).

[anon]

It doesn't necessarily copy the string from the start. You give it a pointer and it starts copying from there. The pointer may well point to the middle of a string.

Now you'll have to figure out how to obtain a pointer to the second character in your string.

It also looks that you'll need to set the null terminator yourself after using strncpy.

[vart]

to copy one character only just use

dest[x] = src[y];

to add nul-char after that

dets[x+1] = '\0';

[rasta_freak]

Maybe:

snprintf(old, 3, "%s", &(new[1]));

?

[pgcrooks]

Humm I shall have to learn more about pointers, never really got my head around the snytax for them. Thanks anyway!

addptr = *indata[2];
strncpy = (oldadd, addptr, 2);

Right, tried that and no luck. Thought it should have set a pointer to the start of what I want in the string but it says incorrect type. Back to work I go...

[rasta_freak]

Humm I shall have to learn more about pointers, never really got my head around the snytax for them. Thanks anyway!

addptr = *indata[2];
strncpy = (oldadd, addptr, 2);

Right, tried that and no luck. Thought it should have set a pointer to the start of what I want in the string but it says incorrect type. Back to work I go...

Try:

snprintf(oldadd, 3, "%s", &(indata[1]));

EDIT: docs says it auto-puts \0 on end !

[anon]

As other people are showing you, you don't obtain the pointer by trying to dereference what is already a char (*str[i]), but by taking the address (&str[i]). Alternatively you can use pointer arithmetic (str + 1).

Also note that the second character is at index 1, not 2.

[pgcrooks]

Try:

strncpy(oldadd, 3, "%s", &(indata[1]));

Ok, thats seems to have compiled ok! Just had to modify the order

strncpy(oldadd, &(indata[1]), 2);

Have about a million other syntax errors to fix before I can actually run the program, lets hope that works!

Can you tell it's the first time I've tried string manipulation, integer work is so much easier lol.

Thanks all.

[rasta_freak]

Ok, thats seems to have compiled ok! Just had to modify the order

strncpy(oldadd, &(indata[1]), 2);

Have about a million other syntax errors to fix before I can actually run the program, lets hope that works!

Can you tell it's the first time I've tried string manipulation, integer work is so much easier lol.

Thanks all.

No, you got my error-post. Use "snprintf()" !!! (look at post again, and sorry about mistake)

[matsp]

No, you got my error-post. Use "snprintf()" !!! (look at post again, and sorry about mistake)

s(n)printf probably takes 30-100 times longer than strncpy()/strncat(), as the process of parsing the input string and such is quite inefficient.

--
Mats

[rasta_freak]

s(n)printf probably takes 30-100 times longer than strncpy()/strncat(), as the process of parsing the input string and such is quite inefficient.

--
Mats

But, then again, fastest method would be:

oldadd[0] = indata[1];
oldadd[1] = indata[2];
oldadd[2] = 0;

EDIT: maybe using 'short' for 2-byte operation.

[pgcrooks]

Thanks guys, got it working in the end. Just used Rasta's assign technique, much easier! I forgot you could do that with single chars, just not with full strings (think that's right).