C语言容易被忽视的函数设计原则基础

目录

• 一、函数设计原则
• 二、总结

一、函数设计原则

• 函数从意义上应该是一个独立的功能模块
• 函数名要在一定程度上反映函数的功能
• 函数参数名要能够体现参数的意义
• 尽量避免在函数中使用全局变量
• 当函数参数不应该在函数体内部被修改时，应加上 const 声明
• 如果参数是指针，且仅作输入参数，则应加上 const 声明，如下：

• 不能省略返回值的类型
• 如果函数没有返回值，那么应声明为 void
• 类型对参数进行有效性检查
• 对于指针参数的检查尤为重要
• 不要返回指向“栈内存”的指针
• 栈内存在函数体结束时被自动释放
• 函数体的规模要小，尽量控制在 80 行代码之内
• 相同的输入对应相同的输出，避免函数带有“记忆”功能
• 避免函数有过多的参数，参数个数尽量控制在 4 个以内
• 有时候函数不需要返回值，但为了增加灵活性，如支持链式表达，可以附加返回值

• 函数名与返回值类型在语义上不可冲突

下面来欣赏一份优秀的代码：

/*******************************************************************************
 * Copyright (c) 2000, 2005 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *     Kevin Cornell (Rational Software Corporation)
 *******************************************************************************/
/* Eclipse Launcher Utility Methods */
#include "eclipseOS.h"
#include "eclipseCommon.h"
#include "eclipseUtil.h"
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/stat.h>
#ifdef _WIN32
#include <direct.h>
#else
#include <unistd.h>
#include <strings.h>
#endif
#define MAX_LINE_LENGTH 256
/* Is the given VM J9 */
int isJ9VM( _TCHAR* vm )
{
	_TCHAR * ch = NULL, *ch2 = NULL;
	int res = 0;
	if (vm == NULL)
		return 0;
	ch = lastDirSeparator( vm );
	if (isVMLibrary(vm)) {
		/* a library, call it j9 if the parent dir is j9vm */
		if(ch == NULL)
			return 0;
		ch[0] = 0;
		ch2 = lastDirSeparator(vm);
		if(ch2 != NULL) {
			res = (_tcsicmp(ch2 + 1, _T_ECLIPSE("j9vm")) == 0);
		}
		ch[0] = dirSeparator;
		return res;
	} else {
		if (ch == NULL)
		    ch = vm;
		else
		    ch++;
		return (_tcsicmp( ch, _T_ECLIPSE("j9") ) == 0);
	}
}
int checkProvidedVMType( _TCHAR* vm )
{
	_TCHAR* ch = NULL;
	struct _stat stats;
	if (vm == NULL) return VM_NOTHING;
	if (_tstat(vm, &stats) == 0 && (stats.st_mode & S_IFDIR) != 0) {
		/* directory */
		return VM_DIRECTORY;
	}
	ch = _tcsrchr( vm, _T_ECLIPSE('.') );
	if(ch == NULL)
		return VM_OTHER;
#ifdef _WIN32
	if (_tcsicmp(ch, _T_ECLIPSE(".dll")) == 0)
#else
	if ((_tcsicmp(ch, _T_ECLIPSE(".so")) == 0) || (_tcsicmp(ch, _T_ECLIPSE(".jnilib")) == 0) || (_tcsicmp(ch, _T_ECLIPSE(".dylib")) == 0))
#endif
	{
		return VM_LIBRARY;
	}
	if (_tcsicmp(ch, _T_ECLIPSE(".ee")) == 0)
		return VM_EE_PROPS;
	return VM_OTHER;
}
/*
 * pathList is a pathSeparator separated list of paths, run each through
 * checkPath and recombine the results.
 * New memory is always allocated for the result
 */
_TCHAR * checkPathList( _TCHAR* pathList, _TCHAR* programDir, int reverseOrder) {
	_TCHAR * c1, *c2;
	_TCHAR * checked, *result;
	size_t checkedLength = 0, resultLength = 0;
	size_t bufferLength = _tcslen(pathList);
	result = malloc(bufferLength * sizeof(_TCHAR));
	c1 = pathList;
    while (c1 != NULL && *c1 != _T_ECLIPSE('\0'))
    {
    	c2 = _tcschr(c1, pathSeparator);
		if (c2 != NULL)
			*c2 = 0;
		checked = checkPath(c1, programDir, reverseOrder);
		checkedLength = _tcslen(checked);
		if (resultLength + checkedLength + 1> bufferLength) {
			bufferLength += checkedLength + 1;
			result = realloc(result, bufferLength * sizeof(_TCHAR));
		}
		if(resultLength > 0) {
			result[resultLength++] = pathSeparator;
			result[resultLength] = _T_ECLIPSE('\0');
		}
		_tcscpy(result + resultLength, checked);
		resultLength += checkedLength;
		if(checked != c1)
			free(checked);
		if(c2 != NULL)
			*(c2++) = pathSeparator;
		c1 = c2;
	}
    return result;
}
_TCHAR * concatStrings(_TCHAR**strs) {
	return concatPaths(strs, 0);
}
_TCHAR * concatPaths(_TCHAR** strs, _TCHAR separator) {
	_TCHAR separatorString[] = { separator, 0 };
	_TCHAR * result;
	int i = -1;
	size_t length = 0;
	/* first count how large a buffer we need */
	while (strs[++i] != NULL) {
		length += _tcslen(strs[i]) + (separator != 0 ? 1 : 0);
	}
	result = malloc((length + 1) * sizeof(_TCHAR));
	result[0] = 0;
	i = -1;
	while (strs[++i] != NULL) {
		result = _tcscat(result, strs[i]);
		if (separator != 0)
			result = _tcscat(result, separatorString);
	}
	return result;
}
/*
 * buffer contains a pathSeparator separated list of paths, check
 * that it contains all the paths given.  Each path is expected to be
 * terminated with a pathSeparator character.
 */
int containsPaths(_TCHAR * str, _TCHAR** paths) {
	_TCHAR * buffer;
	_TCHAR * c;
	int i;
	/* terminate the string with a pathSeparator */
	buffer = malloc((_tcslen(str) + 2) * sizeof(_TCHAR));
	_stprintf(buffer, _T_ECLIPSE("%s%c"), str, pathSeparator);
	for (i = 0; paths[i] != NULL; i++) {
		c = _tcsstr(buffer, paths[i]);
		if ( c == NULL || !(c == buffer || *(c - 1) == pathSeparator))
		{
			/* entry not found */
			free(buffer);
			return 0;
		}
	}
	free(buffer);
	return 1;
}
int isVMLibrary( _TCHAR* vm )
{
	_TCHAR *ch = NULL;
	if (vm == NULL) return 0;
	ch = _tcsrchr( vm, '.' );
	if(ch == NULL)
		return 0;
#ifdef _WIN32
	return (_tcsicmp(ch, _T_ECLIPSE(".dll")) == 0);
#else
	return (_tcsicmp(ch, _T_ECLIPSE(".so")) == 0) || (_tcsicmp(ch, _T_ECLIPSE(".jnilib")) == 0) || (_tcsicmp(ch, _T_ECLIPSE(".dylib")) == 0);
#endif
}
#ifdef AIX
#include <sys/types.h>
#include <time.h>
/* Return the JVM version in the format x.x.x
 */
char* getVMVersion( char *vmPath )
{
    char   cmd[MAX_LINE_LENGTH];
    char   lineString[MAX_LINE_LENGTH];
    char*  firstChar;
    char   fileName[MAX_LINE_LENGTH];
    time_t curTime;
    FILE*  fp;
    int    numChars = 0;
    char*  version  = NULL;
	/* Define a unique filename for the java output. */
    (void) time(&curTime);
    (void) sprintf(fileName, "/tmp/tmp%ld.txt", curTime);
    /* Write java -version output to a temp file */
    (void) sprintf(cmd,"%s -version 2> %s", vmPath, fileName);
    (void) system(cmd);
    fp = fopen(fileName, "r");
    if (fp != NULL)
    {
    	/* Read java -version output from a temp file */
    	if (fgets(lineString, MAX_LINE_LENGTH, fp) == NULL)
    		lineString[0] = '\0';
    	fclose(fp);
    	unlink(fileName);
    	/* Extract version number */
    	firstChar = (char *) (strchr(lineString, '"') + 1);
    	if (firstChar != NULL)
    		numChars = (int)  (strrchr(lineString, '"') - firstChar);
    	/* Allocate a buffer and copy the version string into it. */
    	if (numChars > 0)
    	{
    		version = malloc( numChars + 1 );
    		strncpy(version, firstChar, numChars);
			version[numChars] = '\0';
		}
	}
    return version;
}
/* Compare JVM Versions of the form "x.x.x..."
 *
 *    Returns -1 if ver1 < ver2
 *    Returns  0 if ver1 = ver2
 *    Returns  1 if ver1 > ver2
 */
int versionCmp(char *ver1, char *ver2)
{
    char*  dot1;
    char*  dot2;
    int    num1;
    int    num2;
    dot1 = strchr(ver1, '.');
    dot2 = strchr(ver2, '.');
    num1 = atoi(ver1);
    num2 = atoi(ver2);
    if (num1 > num2)
    	return 1;
	if (num1 < num2)
		return -1;
	if (dot1 && !dot2)   /* x.y > x */
        return 1;
    if (!dot1 && dot2)   /* x < x.y */
        return -1;
    if (!dot1 && !dot2)  /* x == x */
        return 0;
    return versionCmp((char*)(dot1 + 1), (char*)(dot2 + 1) );
}
#endif /* AIX */

二、总结

• C 语言的学习需要勤思考勤动手才能得到
• 提高难点部分为指针的学习
• 指针的本质，指针的运算，指针和数组
• 学习过程可以采用各个击破的方法
• 在一个特定的时间段只重点学习和练习某个主题
• 在熟练掌握C语言的各个特性后再进行项目练习

至此，C 语言进阶剖析学完，完结撒花。

但是，以后路还很远，还需要多加总结，才能真正掌握 C 语言。

到此这篇关于C语言容易被忽视的函数设计原则基础的文章就介绍到这了,更多相关C语言函数设计原则内容请搜索我们以前的文章或继续浏览下面的相关文章希望大家以后多多支持我们！