Function to invert strings in C

Question

Inserts the orig string at the beginning of the dest string, returning dest.

char *strins(char *dest, char *orig)

My code is as follows::

char *strins(char *dest, char *orig)
{
    return strcat(*orig,*dest);
}

main()
{
    char s[] = "World";
    strins(s, "Hello");
    printf(s);
}

The function should work like this:

char s[100] = "Autonoma";
strins(s, "Universidade");
printf(s);  ->  UniversidadeAutonoma

Answer 1

There are several problems in your code.

First, when you define a literal string with char s[] = "World"; you are allocating only the memory space required for that specific number of characters.

Since you want to join two strings, the size will increase, so you need more space. This is solved for example by setting a maximum size with char s[100] = "World";.

Also you can’t modify a literal string, so you can’t do the function the way you did and expect it to work with strins(s, "Hello"); since he won’t be able to modify the literal string "Hello".

Finally, the result of the function strcat is saved in the first parameter, so it would be saved in the orig instead of dest as desired. A strcpy will suffice, though will leave the source variable "dirty", what I don’t know if it’s a problem.

Follow the code with the corrected suggested problems:

#include <stdio.h>
#include <string.h>
char *strins(char *dest, char *orig)
{

    strcat(orig,dest);
    strcpy(dest,orig);
    return dest;
}

int main()
{
    char s[100] = "World";
    char outro[100]= "Hello";
    strins(s,outro);
    printf("%s\n",s);
    return 0;
}

That returns the result:

HelloWorld