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。
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