[diff.lex]

# Annex C (informative) Compatibility [[diff]](./#diff)

## C.7 C++ and C [[diff.iso]](diff.iso#diff.lex)

### C.7.2 [[lex]](lex "5 Lexical conventions"): lexical conventions [diff.lex]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/compatibility.tex#L2746)

**Affected subclause:** [[lex.key]](lex.key)  


**Change:** New Keywords[.](#1.sentence-1)

  


New keywords are added to C++;
see [[lex.key]](lex.key "5.12 Keywords")[.](#1.sentence-2)

  


**Rationale:** These keywords were added in order to implement the new
semantics of C++[.](#1.sentence-3)

  


**Effect on original feature:** Change to semantics of well-defined feature[.](#1.sentence-4)

Any C programs that used any of these keywords as identifiers
are not valid C++ programs[.](#1.sentence-5)

  


**Difficulty of converting:** Syntactic transformation[.](#1.sentence-6)

Converting one specific program is easy[.](#1.sentence-7)

Converting a large collection
of related programs takes more work[.](#1.sentence-8)

  


**How widely used:** Common[.](#1.sentence-9)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/compatibility.tex#L2766)

**Affected subclause:** [[lex.ccon]](lex.ccon)  


**Change:** Type of [*character-literal*](lex.ccon#nt:character-literal "5.13.3 Character literals [lex.ccon]") is changed from int to char[.](#2.sentence-1)

  


**Rationale:** This is needed for improved overloaded function argument type
matching[.](#2.sentence-2)

[*Example [1](#example-1)*: int function( int i );int function( char c );

function( 'x' );

It is preferable that this call match the second version of
function rather than the first[.](#2.sentence-3)

— *end example*]

  


**Effect on original feature:** Change to semantics of well-defined feature[.](#2.sentence-4)

C programs which depend onsizeof('x') == sizeof(int) will not work the same as C++ programs[.](#2.sentence-5)

  


**Difficulty of converting:** Simple[.](#2.sentence-6)

  


**How widely used:** Programs which depend upon sizeof('x') are probably rare[.](#2.sentence-7)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/compatibility.tex#L2794)

**Affected subclause:** [[lex.string]](lex.string)  


**Change:** Concatenated [*string-literal*](lex.string#nt:string-literal "5.13.5 String literals [lex.string]")*s* can no longer have
conflicting [*encoding-prefix*](lex.ccon#nt:encoding-prefix "5.13.3 Character literals [lex.ccon]")es[.](#3.sentence-1)

  


**Rationale:** Removal of non-portable feature[.](#3.sentence-2)

  


**Effect on original feature:** Concatenation of [*string-literal*](lex.string#nt:string-literal "5.13.5 String literals [lex.string]")*s* with different [*encoding-prefix*](lex.ccon#nt:encoding-prefix "5.13.3 Character literals [lex.ccon]")es
is now ill-formed[.](#3.sentence-3)

  


**Difficulty of converting:** Syntactic transformation[.](#3.sentence-4)

  


**How widely used:** Seldom[.](#3.sentence-5)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/compatibility.tex#L2809)

**Affected subclause:** [[lex.string]](lex.string)  


**Change:** String literals made const[.](#4.sentence-1)

  


The type of a [*string-literal*](lex.string#nt:string-literal "5.13.5 String literals [lex.string]") is changed
from “array of char”
to “array of const char”[.](#4.sentence-2)

The type of a UTF-8 string literal is changed
from “array of char”
to “array of const char8_t”[.](#4.sentence-3)

The type of a UTF-16 string literal is changed
from “array of *some-integer-type*”
to “array of const char16_t”[.](#4.sentence-4)

The type of a UTF-32 string literal is changed
from “array of *some-integer-type*”
to “array of const char32_t”[.](#4.sentence-5)

The type of a wide string literal is changed
from “array of wchar_t”
to “array of const wchar_t”[.](#4.sentence-6)

  


**Rationale:** This avoids calling an inappropriate overloaded function,
which might expect to be able to modify its argument[.](#4.sentence-7)

  


**Effect on original feature:** Change to semantics of well-defined feature[.](#4.sentence-8)

  


**Difficulty of converting:** Syntactic transformation[.](#4.sentence-9)

The fix is to add a cast:char* p = "abc"; // valid in C, invalid in C++void f(char*) {char* p = (char*)"abc"; // OK, cast added f(p);
 f((char*)"def"); // OK, cast added}  

**How widely used:** Programs that have a legitimate reason to treat string literal objects
as potentially modifiable memory are probably rare[.](#4.sentence-11)