Changeset 195f43d for doc/theses/mike_brooks_MMath/background.tex

Timestamp:

Mar 13, 2025, 9:21:17 AM (2 weeks ago)

Author:

Peter A. Buhr <pabuhr@…>

Branches:

master

Children:

3bd9508

Parents:

3483185

Message:

start proofreading string chapter

File:

• doc/theses/mike_brooks_MMath/background.tex (modified) (2 diffs)

doc/theses/mike_brooks_MMath/background.tex ¶

@@ -468 +468 @@
 \VRef[Figure]{f:ContiguousNon-contiguous} shows a powerful extension made in C99 for manipulating contiguous \vs non-contiguous arrays.\footnote{C90 also supported non-contiguous arrays.}
 For contiguous-array (including VLA) arguments, C99 conjoins one or more of the parameters as a downstream dimension(s), \eg @cols@, implicitly using this parameter to compute the row stride of @m@.
-There is now sufficient information to support subscript checking along the columns to prevent buffer-overflow problems, but subscript checking is not provided.
+There is now sufficient information to support array copying and subscript checking along the columns to prevent changing the argument or buffer-overflow problems, but neither feature is provided.
 If the declaration of @fc@ is changed to:
 \begin{cfa}
@@ -1221 +1221 @@
 This representation means that there is no real limit to how long a string can be, but programs have to scan one completely to determine its length.~\cite[p.~36]{C:old}
 \end{quote}
-Unfortunately, this design decision is both unsafe and inefficient.
-It is common error in C to forget the storage in a character array for the terminator or overwrite the terminator, resulting in array overruns in string operations.
-The need to repeatedly scan an entire string to determine its length can result in significant cost, as it is impossible to cache the length in many cases.
+This property is only preserved by the compiler with respect to character constants, \eg @"abc"@ is actually @"abc\0"@, \ie 4 characters rather than 3.
+Otherwise, the compiler does not participate, making string operations both unsafe and inefficient.
+For example, it is common in C to: forget that a character constant is larger than it appears during manipulation, that extra storage is needed in a character array for the terminator, or that the terminator must be preserved during string operations, otherwise there are array overruns.
+Finally, the need to repeatedly scan an entire string to determine its length can result in significant cost, as it is impossible to cache the length in many cases, \eg when a string is passed into another function.
 
 C strings are fixed size because arrays are used for the implementation.