implicit declaration of function ‘strrev’

Question

Any ideas on why when I try to compile this code to check if a line from the file atadata I get the warning:

warning: implicit declaration of function ‘strrev’ [-Wimplicit-function-declaration]

CODE

#include <stdio.h>
#include <string.h>
int main(){
    char palindromes[100];
    char reverse[100];
    FILE *atadata = fopen("atadata","r");
    while (fgets(palindromes,sizeof(palindromes),atadata) != NULL){
        strcpy(reverse,palindromes);
        strrev(reverse);
        if( strcmp(atadata,reverse) == 0)
        fputs(atadata, stdout);
    }
    fclose(atadata);
    return 0;
}

Solution 1

If you are compiling in Linux, then strrev() is not part of string.h. The linked question contains an answer linking to source for an implementation you can bring into your own code directly.

Solution 2

char *strrev(char *str){
    char c, *front, *back;
    if(!str || !*str)
        return str;
    for(front=str,back=str+strlen(str)-1;front < back;front++,back--){
        c=*front;*front=*back;*back=c;
    }
    return str;
}

Solution 3

Incase some of the other peices of code are hard to read or you do not know how to use pointers, here is a short script to reverse a string.

#include <stdio.h>
#include <string.h>
int main(void)
{
// Start here
char String1[30] = "Hello",reversed[30];
int i;
long int length = strlen(String1);
//Reverse string
for(i=0; i<length; ++i)
{
    reversed[length-i-1] = String1[i];
}
printf("First string %s\n",String1);
printf("Reversed string %s\n",reversed);
// To here if you want to copy and paste into your code without making functions 
return 0;
}

Comments

[Martin James]

Is there a definition for it in string.h?

[David C. Rankin]

There is no strrev unless you have written one. (then you need to include the header with your declaration)

[The Paramagnetic Croissant]

@SeanO'Brien You open a text editor, type in the necessary code, save it as a text file and compile it using a C compiler.

[Manjunath N]

This link might be useful from Stack overflow stackoverflow.com/questions/8534274/…

[Alex Reynolds]

That's the same link that is in my answer.

[Manjunath N]

Oh! i didn't observe that's good solution actually.

[pasignature]

This is punk of readable coding style. I love simplicity.

[Harshit Gangwar]

Works for me. !