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In C, the functions strcmp and memcmp perform a three-way comparison between strings and memory buffers, respectively. They return a negative number when the first argument is lexicographically smaller than the second, zero when the arguments are equal, and a positive number otherwise.
Tests if two strings are equal. See also #Compare and #Compare. Note that doing equality checks via a generic Compare with integer result is not only confusing for the programmer but is often a significantly more expensive operation; this is especially true when using "C-strings".
COBOL uses the STRING statement to concatenate string variables. MATLAB and Octave use the syntax "[x y]" to concatenate x and y. Visual Basic and Visual Basic .NET can also use the "+" sign but at the risk of ambiguity if a string representing a number and a number are together. Microsoft Excel allows both "&" and the function "=CONCATENATE(X,Y)".
Structural equality (that is, their contents are the same). which may be either shallow (testing only immediate subparts), or deep (testing for equality of subparts recursively). A simple way to achieve this is through representational equality: checking that the values have the same representation.
For symmetric comparisons, such as equality, swapping the left and right operands does not change the behavior of the program. In programming languages that use a single equals sign ( = ) for assignment expressions, one might mistakenly write an assignment expression where an equality comparison was intended.
In computer science, string interning is a method of storing only one copy of each distinct string value, which must be immutable. [1] Interning strings makes some string processing tasks more time-efficient or space-efficient at the cost of requiring more time when the string is created or interned.
If the strings represent potentially isomorphic structures such as graphs, normalizing in this way allows for simple equality checking. [1] A common implementation trick when dealing with circular strings is to concatenate the string to itself instead of having to perform modular arithmetic on the string indices.
A simple and inefficient way to see where one string occurs inside another is to check at each index, one by one. First, we see if there is a copy of the needle starting at the first character of the haystack; if not, we look to see if there's a copy of the needle starting at the second character of the haystack, and so forth.