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String.h

As explained in Modern C, Third Edition

string.h is the C standard header that declares functions for manipulating strings and related memory sequences.

string.h is the C standard header for manipulating character arrays, null-terminated strings, and related memory sequences. Its functions divide into two naming families: mem functions operate on a specified number of elements, while str functions expect null-terminated strings. section 6.1.5 section 8.9

The central safety and behavior rules are:

  • Use memcpy(target, source, len) for a known element count; the source and target arrays must be distinct. section 6.1.5
  • Use memcmp and memchr for bounded comparison and search; neither operation requires a null-terminated string. section 6.1.5
  • Use strlen only when the array contains a terminating zero character; it returns that character's position, not the array's capacity. section 6.1.5
  • Use strcpy only with a terminated source and a target large enough for the copied string; strdup allocates storage before copying. section 6.1.5

Copying a program name

The example computes strlen(argv[0]), allocates an array with one additional element for the terminating zero, copies the characters with memcpy, and checks the result with strcmp. The extra element is essential: the copied character count excludes the terminator. section 6.1.5

How Modern C, Third Edition covers it

How deep it goes
Defines function families, termination rules, size constraints, and a combined copying example without descending into implementation internals.
Examples
Uses argv[0], strlen, memcpy, strcmp, and a variable-length array to verify a copied program name.
What it assumes
Assumes familiarity with char arrays and pointers while making null termination and array-capacity requirements explicit.
What you can do after
Apply string.h functions to copy, compare, search, and measure terminated strings or bounded character arrays.
How it connects
Connects character arrays, null-terminated strings, memory operations, command-line arguments, variable-length arrays, and the C standard library.
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