QUESTION 33 · String Operations

Name four standard string functions and their purposes.

2 marks

Answer

strlen finds length, strcpy copies, strcat appends and strcmp compares strings.

They are declared in string.h.
Their arguments must satisfy termination, storage and other function-specific requirements.

Explain the main string library functions and their precautions.

5 marks

Answer in brief

The string.h header declares common operations on null-terminated strings and memory. Each function still requires valid arguments and sufficient storage.

Main functions

strlen(s) returns the number of bytes before the null terminator as size_t.
strcpy(destination, source) copies the source and its terminator.
strcat(destination, source) appends the source after the destination’s existing string.
strcmp(a, b) compares two strings and returns a negative, zero or positive value.
strchr(s, ch) locates the first matching character, or returns NULL when absent.

Capacity requirements

strcpy needs enough writable destination positions for source length plus one. strcat needs enough for both lengths plus one, and destination must already contain a valid string. These functions do not receive the destination’s capacity and cannot automatically grow it.

Overlap and bounded forms

strcpy and strcat require non-overlapping source and destination strings. For overlapping regions within one array, memmove is designed for moving a specified byte count safely. strncpy is not a general guarantee of termination: if the source is at least the specified count, the copied result is not automatically terminated.

Comparison and length

Use strcmp rather than == to compare text contents. Check only its result’s sign, not an assumed exact -1 or 1. Use %zu for the size_t returned by strlen. The length excludes the terminator, while required storage includes it.

Complexity

strlen and strcpy perform work proportional to the relevant string length. A single strcat must find the destination end and copy the source, giving O(d + s) work. strcmp examines a prefix until a difference or end is reached, up to O(min(m, n) + 1) byte comparisons. No growing auxiliary array is required by these basic operations.

Reference table

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String function requirements
Function	Purpose	Key requirement
strlen	Count bytes before terminator	Valid terminated source
strcpy	Copy with terminator	Enough capacity; no overlap
strcat	Append source	Terminated destination; enough space; no overlap
strcmp	Compare contents	Both sources terminated
strchr	Find character	Valid terminated source
memmove	Move specified byte count	Valid source/destination ranges; overlap allowed