C語言最大難點(diǎn)揭秘：編程的禍根！

引言

正確的內(nèi)存管理的重要性

內(nèi)存錯(cuò)誤的類別

voidf1(char*explanation)
{
charp1;

p1=malloc(100);
(void)sprintf(p1,
"Thef1erroroccurredbecauseof'%s'.",
explanation);
local_log(p1);
}

intgetkey(char*filename)
{
FILE*fp;
intkey;

fp=fopen(filename,"r");
fscanf(fp,"%d",&key);
returnkey;
}

voidf2(intdatum)
{
int*p2;

/*Uh-oh!Noonehasinitializedp2.*/
*p2=datum;
...
}

/*Allocateonce,freetwice.*/
voidf3()
{
char*p;

p=malloc(10);
...
free(p);
...
free(p);
}

/*Allocatezerotimes,freeonce.*/
voidf4()
{
char*p;

/*Notethatpremainsuninitializedhere.*/
free(p);
}

voidf8()
{
structx*xp;

xp=(structx*)malloc(sizeof(structx));
xp.q=13;
...
free(xp);
...
/*Problem!There'snoguaranteethat
thememoryblocktowhichxppoints
hasn'tbeenoverwritten.*/
returnxp.q;
}

內(nèi)存編程的策略

/********
*...
*
*Notethatanyfunctioninvokingprotected_file_read()
*assumesresponsibilityeventuallytofclose()its
*returnvalue,UNLESSthatvalueisNULL.
*
********/
FILE*protected_file_read(char*filename)
{
FILE*fp;

fp=fopen(filename,"r");
if(fp){
...
}else{
...
}
returnfp;
}

/*******
*...
*
*Notethatthereturnvalueofget_messagepointstoa
*fixedmemorylocation.DoNOTfree()it;rememberto
*makeacopyifitmustberetained...
*
********/
char*get_message()
{
staticcharthis_buffer[400];

...
(void)sprintf(this_buffer,...);
returnthis_buffer;
}


/********
*...
*Whilethisfunctionusesheapmemory,andso
*temporarilymightexpandtheover-allmemory
*footprint,itproperlycleansupafteritself.
*
********/
intf6(char*item1)
{
my_classc1;
intresult;
...
c1=newmy_class(item1);
...
result=c1.x;
deletec1;
returnresult;
}
/********
*...
*Notethatf8()isdocumentedtoreturnavalue
*whichneedstobereturnedtoheap;asf7thinly
*wrapsf8,anycodewhichinvokesf7()mustbe
*carefultofree()thereturnvalue.
*
********/
int*f7()
{
int*p;

p=f8(...);
...
returnp;
}

staticchar*important_pointer=NULL;
voidf9()
{
if(!important_pointer)
important_pointer=malloc(IMPORTANT_SIZE);
...
if(condition)
/*Ooops!Wejustlostthereference
important_pointeralreadyheld.*/
important_pointer=malloc(DIFFERENT_SIZE);
...
}

intmain()
{
charp[5];
strcpy(p,"Hello,world.");
puts(p);
}

結(jié)束語