C语言与Pascal语言对比分析：1981年经典研究

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"C语言与Pascal语言的比较分析——1982年Bell Laboratories研究" 这篇文章是1982年由Bell Laboratories的研究员Alan R. Feuer和Narain H. Gehani发表在《Computer Surveys》杂志上的研究，主要探讨了C语言和Pascal语言在设计哲学、数据类型处理、编程特性、程序质量以及在不同应用领域的适用性等方面的差异与相似之处。 C语言，由Dennis Ritchie于1972年设计，最初是为了编写Unix操作系统而诞生的。它以其高效、灵活和对底层硬件的接近性而著名。C语言的特点包括： 1. **底层控制**：C语言提供了对内存和硬件的直接访问，允许程序员进行低级别的内存管理和系统编程。 2. **结构化编程**：C支持结构化编程，通过函数、循环和选择结构，使得代码组织清晰，易于理解和维护。 3. **类型系统**：C语言有丰富的数据类型，包括基本类型（如int、char、float、double等）、指针类型和复合类型（如结构体和联合体）。 4. **动态内存管理**：C语言中的malloc和free函数允许在运行时动态分配和释放内存。 5. **预处理器**：C语言的预处理器（#include、#define等）用于宏定义和文件包含，增强了代码的可扩展性。 Pascal语言，由Niklaus Wirth于1968年设计，旨在提供一个简洁、清晰且易于学习的编程语言，适合教学和科学计算。Pascal的特点包括： 1. **形式严谨**：Pascal具有严格的语法和语义，有助于减少编程错误。 2. **面向过程**：Pascal支持结构化编程，但没有内置的面向对象特性。 3. **数据类型**：Pascal有固定的预定义数据类型，并允许用户自定义枚举类型和记录类型，但没有C语言中的指针。 4. **模块化**：Pascal的程序可以分解为若干个独立的单元（如程序、子程序和函数），便于代码重用和组织。 5. **编译器优化**：Pascal编译器通常能生成高效的代码，但不如C语言那样对底层硬件的控制精细。在比较中，Feuer和Gehani可能会讨论到以下几点： 1. **设计哲学**：C语言强调效率和灵活性，而Pascal更注重清晰性和教育性。 2. **数据类型处理**：C的指针和动态内存管理提供了更多灵活性，但可能导致错误；Pascal的数据类型系统更为安全，但缺乏C的灵活性。 3. **编程效率**：C可能更适合快速开发和调试，而Pascal可能需要更多时间来编写，但代码可能更稳定。 4. **应用领域**：C语言在系统编程、嵌入式系统和游戏开发中广泛使用，而Pascal在教育、科学计算和小型应用程序中受欢迎。这篇文章对了解两种语言的历史地位和特点具有重要价值，对于软件工程师和计算机科学家来说，理解这些语言的设计决策和优缺点对于选择合适的工具进行项目开发至关重要。

• A. R. Feuer and N. H. Gehani

strongly typed language. It is not perfect in

this regard because its strong typing can be

breached, by means of the variant record

mechanism, for example, and through rou-

tines passed as parameters. Although C is

a typed language, it is not strongly typed.

It was designed to give the programmer the

ability to manipulate data type represen-

tations. It provides several ways for viewing

the representation of an object as different

types, as in the case of unions, pointers,

parameter passing, and structure compo-

nent names.

A provision to breach strong typing is

necessary in any programming language

used for systems programming. However,

instead of including several different facili-

ties that each allow bypassing of the strong

typing mechanism, it would be better to

provide one facility especially designed for

this purpose. Then breaches of strong typ-

ing could be isolated and easily located. For

example, Ada provides the user with a ge-

netic function UNCHECKED CONVER-

SION for breaching strong typing. Unfor-

tunately, in C, typing can be breached in

several ways by means of representation

viewing.

Another difference in the type philoso-

phies of the two languages is their treat-

ment of implicit conversions. The only im-

plicit conversions allowed in PASCAL are

those that do not result in any loss of infor-

mation, as in converting from subranges to

their parent ranges and from integers to

reals (the latter is not quite correct for on

some machines not all integers can be rep-

resented as reals). For conversions between

other types, PASCAL provides type trans-

fer functions that must be called explicitly.

On the other hand, C allows implicit con-

version between any of its basic types or

pointers. The Portable C Compiler, how-

ever, does

warn

the user of implicit conver-

sions involving pointers.

PASCAL's handling of types allows me-

chanical detection of more errors than does

C's, and also prevents certain security vi-

olations, one of the most important contri-

butions of high-level languages [HORN79].

Additionally, Liskov [LISK76] advocates

that implicit conversions should almost

never be permitted even if we understand

mathematically that the conversion makes

sense, because conversions make programs

more difficult to understand. On the other

hand, PASCAL's treatment of types can

occasionally lead to problems, as in the case

of arrays. Since PASCAL considers the ar-

ray size to be part of the type of the array,

one cannot write a routine that accepts

arrays with different numbers of elements.

For example, one cannot write a routine

sort

to sort arrays of different sizes. This is

a serious handicapfi

The value of strong typing is being in-

creasingly appreciated by the C commu-

nity. Implementations of C are becoming

stricter in their treatment of types. In ad-

dition, a utility program

lint

is available

that analyzes C programs to look for viola-

tions of strong typing and other potential

sources of errors, such as using a variable

before it is initialized.

Both languages allow the user to define

new types. However, both C and PASCAL

have ignored the issue of type equivalence.

This is a detriment to program portability

since different implementations may use

different type equivalence strategies (e.g.,

name versus structural type equivalence

[WELS77]).

We conclude that PASCAL, by being

restrictive, emphasizes program reliability

and readability, while C, by its absence of

restrictions, emphasizes programmer flexi-

bility.

3. SUMMARY AND COMPARISON OF

FEATURES

This section contains a feature-by-feature

comparison of C and PASCAL. We assume

that the reader is familiar with program-

ming language concepts, but not necessarily

with either C or PASCAL. For this reason,

we describe each language feature before

discussing it. An informal syntax summary

of the languages is given in Table 1, which

presents how most of the similar facilities

in C and PASCAL are used. Items desig-

nating syntactic classes are in italics and

items surrounded by oversized square

brackets are optional. The italics conven-

tion is followed throughout the paper.

6 Solutions to ehminate this problem have been pro-

posed by Wucth [WIRT75] and others [ISO81].

Computing Surveys, Vol 14, No 1, March 1982

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