error: invalid operands to binary + char *

Question

Possible Duplicate:
C String Concatenation

have the following code:

        char *doencode(const unsigned char *input, int length)
        {
        //irrelevant code
        }

        char *fname, *lname;
        char *encoded, *name;

        name = fname + "|" + lname;
        encoded = doencode(name, 30);

and I get this error: invalid operands to binary +

How can I combine fname & | & lname?

Even if it did compile, it wouldn't work. `name` is not allocated anywhere. — netcoder, Jan 08 '13 at 16:24

score 8 · Accepted Answer · answered Jan 08 '13 at 16:23

8

You cannot concatenate char* and char[] (the "|") or any permutation of using +. Use strncat() or snprintf() instead and ensure the destination buffer has enough memory to store the final string.

answered Jan 08 '13 at 16:23

hmjd

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will it be easier if I replace | with \0 ? – Sam Reina Jan 08 '13 at 16:41
@SamReina, nope. You still need to use a function to concatenate strings. Replacing the `"|"` with a `"\0"` changes nothing regarding the types involved. – hmjd Jan 08 '13 at 16:44

MOHAMED · Answer 2 · 2013-01-08T17:32:40.820

4

the C is not like java script. This is not correct in c:

name = fname + "|" + lname;

you can do it in this way:

sprintf(name,"%s|%s", fname, lname);

The name pointer should be pointed to sufficient memory space.

name = malloc(strlen(fname)+strlen(lname) + 2);

+2: +1 for "|" and +1 for null at the end of the string

Example

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int main()
{
    char *fname, *lname, *name;

    printf("Enter your first name: ");
    scanf ("%ms", &fname);

    printf("Enter your last name: ");
    scanf (" %ms", &lname);

    name = malloc(strlen(fname)+strlen(lname) + 2);
    sprintf(name,"%s|%s", fname, lname);

    printf("name = %s\n",name);

}

edited Jan 08 '13 at 17:32

answered Jan 08 '13 at 16:22

MOHAMED

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This assumes that `name` is pointing at enough space, i.e. it must be a valid pointer and there will be no bounds-checking. – unwind Jan 08 '13 at 16:23
indeed, I will update my answer with that – MOHAMED Jan 08 '13 at 16:24

score 0 · Answer 3 · answered Jan 08 '13 at 16:23

0

You can't simply add strings together in C because strings are actually just pointers to character arrays. What you have to do is allocate storage for a new string and copy the two strings per character into it.

answered Jan 08 '13 at 16:23

Telgin

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error: invalid operands to binary + char *

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