attach second text array on given position

Question

How can i attach one text array to another text array in c on a given position. For example from input user enters 2 arrays and one digit which is the position.

( _ is empty space )
first: hi my name is ,i learn c
second: Jacob_
pos: 14
result hi my name is jacob ,i learn c

here is my code

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

void attach(char *a,char *b,char*c,int pos){
    int i,j;
    for(i = 0; i < pos;i++){
        *(c+i) = *(a+i);

    }
    int lenB = strlen(b);
    for(i = pos+1;i < lenB;i++){
          *(c+i) = *(b+i);
    }
    int lenRes = lenB+pos;
    int lenA = strlen(a);
    for(i = lenRes;i < lenA;i++){
        *(c+i) = *(a+i);
    }

    puts(c);
}

int main()
{
    char a[1000],b[1000],c[1000];
    gets(a);
    gets(b);
    int pos;
    scanf("%d",&pos);
    attach(a,b,c,pos);
    return 0;
}

I suspect you'll find a bust in your logic at `for(i = lenRes;i < lenA;i++) *(c+i) = *(a+i);` , and running your code in a debugger and watching what happens might confirm that. And fyi, this would be a whole lot easier with just pointers (which I think may be the point of the exercise in the first place). — WhozCraig, Jan 03 '22 at 20:43
[never use `gets`](https://stackoverflow.com/questions/1694036/why-is-the-gets-function-so-dangerous-that-it-should-not-be-used) — yano, Jan 03 '22 at 20:45
As-mentioned in my prior comment, using just pointers to fill from a to pos, then fill from b, and finally finish filling from a, significantly cleans up the code. [See example here](https://godbolt.org/z/T7Wr1n5qP). — WhozCraig, Jan 03 '22 at 21:58

score 1 · Accepted Answer · answered Jan 03 '22 at 20:52

Most of your logic for accessing the strings or doing the loops was just wrong. For example, your second for loop would have zero iterations whenever the user specifies a pos such that pos + 1 >= lenB, so that can't be right. You also forgot to add a null termination character at the end of the string.

I kept the basic structure of your program, but cleaned up some minor things and fixed the logic.

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

void attach(const char * a, const char * b, char * c, int pos) {
  int i;
  for (i = 0; i < pos; i++) {
    c[i] = a[i];
  }
  int lenB = strlen(b);
  for (i = 0; i < lenB; i++) {    // I fixed this line
    c[pos + i] = b[i];            // I fixed this line
  }
  int lenA = strlen(a);
  for (i = pos; i < lenA; i++) {  // I fixed this line
    c[i + lenB] = a[i];           // I fixed this line
  }
  c[lenA + lenB] = 0;             // I added this
}

int main()
{
  char c[1000];
  attach("Hi my name is , I learn C", "David", c, 14);
  puts(c);   // I moved this to a better place
}

This program produces the output "Hi, my name is David, I learn C".

By the way, c[i] is equivalent to *(c + i), so use whichever syntax you find more readable.

Also, to help you find better answers with Internet searches in the future, this operation is not usually called "attach". It is usually called "insert". And we don't call these things "text arrays", we call them "strings". So a better way to ask your question is: "How can I insert a string into the middle of another string?"

attach second text array on given position

1 Answers1