String Comparison Using '==' Vs. 'Strcmp()'

String comparison using '==' vs. 'strcmp()'

The reason to use it is because strcmp

returns < 0 if str1 is less than str2; > 0 if str1 is greater than str2, and 0 if they are equal.

=== only returns true or false, it doesn't tell you which is the "greater" string.

strcmp or string::compare?

For C++, use std::string and compare using string::compare.

For C use strcmp. If your (i meant your programs) strings (for some weird reason) aren't nul terminated, use strncmp instead.

But why would someone not use something as simple as == for std::string
?

Why use strcmp instead of == in C++?

strcmp compares the actual C-string content, while using == between two C-string is asking if these two char pointers point to the same position.

If we have some C-string defined as following:

char string_a[] = "foo";
char string_b[] = "foo";
char * string_c = string_a;

strcmp(string_a, string_b) == 0 would return true, while string_a == string_b would return false. Only when "comparing" string_a and string_c using == would return true.

If you want to compare the actual contents of two C-string but not whether they are just alias of each other, use strcmp.

For a side note: if you are using C++ instead of C as your question tag shows, then you should use std::string. For example,

std::string string_d = "bar";
std::string string_e = "bar";

then string_d == string_e would return true. string_d.compare(string_e) would return 0, which is the C++ version of strcmp.

Storing/Comparing u_char passed to function

snprintf() will use the same format string and parameters as the printf() call you already have working.

char NewString[] = "00:00:00:00:00:00";  // initializing with this string is just a lazy
                                         //   way to get the right amount of storage

snprintf( NewString, sizeof( NewString), "%2.2x:%2.2x:%2.2x:%2.2x:%2.2x:%2.2x", var[0], var [1], var[2], var[3], var[4], var[5]);

Using strcmp to compare strings vs. comparing characters directly

Comparing characters directly is pretty vile and fragile code. Depending on the compiler and architecture, it might also be harder to optimize.

On the other hand, your copy is a waste - it does nothing useful.

Just check the string is at least long enough (or exactly the right length, but any way not too short) and strncmp (or memcmp) it in place.

#define COMPARE(IN, OFF, SUB) memcmp(IN+OFF, SUB, sizeof(SUB)-1)

input = "BANANASingorethispartAPPLESignorethisalsoORANGES";

if (COMPARE(input,  0, "BANANAS") == 0 &&
    COMPARE(input, 21, "APPLES" ) == 0 &&
    COMPARE(input, 40, "ORANGES") == 0) )
{

String.equals versus ==

Use the string.equals(Object other) function to compare strings, not the == operator.

The function checks the actual contents of the string, the == operator checks whether the references to the objects are equal. Note that string constants are usually "interned" such that two constants with the same value can actually be compared with ==, but it's better not to rely on that.

if (usuario.equals(datos[0])) {
    ...
}

NB: the compare is done on 'usuario' because that's guaranteed non-null in your code, although you should still check that you've actually got some tokens in the datos array otherwise you'll get an array-out-of-bounds exception.

Comparing two strings, problems with strcmp

strcmp returns 0 if the two strings are exactly the same to accomplish what you want to do

Use :

strstr(s2 , "login:")

(It return NULL if the string doesn't exist in s2)

or

strncmp(s2 , "login:" , 6)

This will compare the first 6 characters (if s2 begins with "login:" , it will return 0)

---

Related Topics