compare strings with strcmp function works different

Question

I'm comparing two strings with strcmp in the following manner:

long t=1011;
char tc[10], tcr[10];
ltoa(t,tc,10);
cout<<tc<<endl;  //prints 1011
strcpy(tcr, strrev(tc));
cout<<tcr<<endl; //prints 1101
cout<<strcmp(tc,tcr);

This gives me a result of 0, which indicates that the strings are equal. However, when I try:

cout<<strcmp("1011", "1101"); // prints -1 thats okay

I get the expected value of -1. What's am I doing wrong? I am using devc++ compiler version 4.9.9.2

strrev function changes tc string (it works on tc array). After strrev and strcpy tcr is equal to tc. — AdamF, Jun 05 '14 at 18:07

score 2 · Accepted Answer · answered Jun 05 '14 at 18:09

It depends on how function strrev is defined, If it reverses the argument in place then the result is expected because tc was reversed.

For example function strrev can be declared the following way

char * strrev( char *s );

and the return value and the value of the argument will be equal.

Take into account that strrev is not a standard function.

score 0 · Answer 2 · answered Jun 05 '14 at 18:12

If you change your code like so:

long t=1011;
char tc[10], tcr[10];
ltoa(t,tc,10);
strcpy(tcr, strrev(tc));
cout<<tc<<endl; 
cout<<tcr<<endl;
cout<<strcmp(tc,tcr);

then you'll see that tc and tcr are the same. strrev reverses the input string in place, and 1101 is printed twice.

compare strings with strcmp function works different

2 Answers2