How do I pass an array as an argument to a function? - c

Question

I have read the post here on the same subject, but it doesn't seem to have the solution to my problem.
If I need to write a function str_reverse() which reverses any string passed to it, how can I go about it? Just as the person who asked the question I linked above, the following code
#include <stdio.h>
#include <string.h> //for strlen
#define maxL 300 //Max String Length
void str_reverse(char);
int main(){
//Variables
char x[maxL];
//User Prompt
printf("Enter a string no longer than %d characters: ", maxL);
gets(x);
str_reverse(x);
//Return Statement
return 0;
}
void str_reverse(char x){
int i, l;
l = strlen(x);
printf("In reverse: ");
for(i=l-1; i>=0; i--)
printf("%c",x[i]);
}
gives me an error. How can I create a program which allows me to reverse the string?

Answer 1

You are passing fine but the function isn't receiving properly. Change it to:
void str_reverse(char *x){
..
}
and the prototype to:
void str_reverse(char*);
Also, gets() is dangerous and should never be used. Use fgets() instead:
if( fgets(x, sizeof x, stdin) == NULL) { /* failure */ }
x[strcspn(x,"\n")] = 0; // to remove the trailing newline, if any.

Answer 2

Your can pass array as type arr[] or as type * pointer. you will have to pass length as an argument to your string reverse function. New declaration of string reverse will look like this:
void str_reverse(char *x,int length)
or
void str_reverse(char x[],int length)
for more information you can follow Length of array in function argument

Answer 3

A function parameter declared as an array is adjusted to pointer to array element.
Thus these function declarations are equivalent and declare the same one function
#define maxL 300
void str_reverse(char[maxL]);
or
void str_reverse(char[10]);
or
void str_reverse(char[1000]);
or
void str_reverse(char[]);
or
void str_reverse( char *);
And on the other hand when an array is passed as an argument to a function it is implicitly converted to pointer to its first element.
So this function call
char x[maxL];
//...
str_reverse(x);
can be imagine like
char x[maxL];
//...
char *tmp = x;
str_reverse(tmp);
Take into account that function gets is unsafe and is not supported by the C Standard any more.
Use instead standard function fgets
Also it is better if the function returned pointer to its first character.
Your function does not try to reverse a string. It tries to output a string in the reverse order.
So the function that indeed reverses a string can be written like
char * str_reverse( char *s )
{
size_t n = strlen( s );
for ( size_t i = 0; i < n / 2; i++ )
{
char c = s[i];
s[i] = s[n- i-1];
s[n-i-1] = c;
}
return s;
}
Here is a demonstrative program
#include <stdio.h>
#include <string.h>
#define maxL 300 //Max String Length
char * str_reverse( char *s )
{
size_t n = strlen( s );
for ( size_t i = 0; i < n / 2; i++ )
{
char c = s[i];
s[i] = s[n- i-1];
s[n-i-1] = c;
}
return s;
}
int main( void )
{
//Variables
char s[maxL];
//User Prompt
printf("Enter a string no longer than %zu characters: ", maxL);
fgets( s, maxL, stdin );
s[strcspn( s, "\n" )] = '\0';
puts( str_reverse( s ) );
return 0;
}
Its output might look like
Enter a string no longer than 300 characters: Hello, World!
!dlroW ,olleH

Answer 4

You can achieve this by many different ways:
Option-1
Formal parameters as a pointer −
void myFunction(char *param) {
.
.
.
}
Option-2
Formal parameters as a sized array −
void myFunction(char param[10]) {
.
.
.
}
Option-3
Formal parameters as an unsized array −
void myFunction(char param[]) {
.
.
.
}