关于C++的异常的问题(页 1) - C/C++ (STL/boost) - Linux伊甸园论坛

xplayer512 发表于 2007-7-18 15:27

关于C++的异常的问题

　　我用g++编译的c++程序。不知道在catch里应该是catch(exception e)还是(exception& e)?(《C++完全参考》里用的是普通的参数，ibm网站上的知识库里的程序用的是引用参数）我不知道该用哪个了。`"KmH+Qq
　　还有就是抛出异常时throw SocketException(m_errno);里面带参数就出错？非要这样才行throw SocketException();？而且出错时候居然是语法错误。}J{ Aa:d\
　　请高手们指点一下。

dearvoid 发表于 2007-7-18 20:11

如果 throw 出来的 exception 的类型是 E 的话, 应该 catch(E e) 或者 catch(E & e), 举例:-K._V-M[
[code]-F"wb/XTrd2~
-(dearvoid@LinuxEden:tty3)-(~/void/c++)-W]/tAct
[4013 0] # cat exception.cc:O#r|!] m
#include <iostream>
c%q`W-P
using namespace std;P9R7q*}1XfR0{#b WS

class MyException {
public:
MyException() {}
MyException(const string & s) : errMsg(s) {}+A;Xxvh*n'I&M

const string & getMsg()/X7bMc-n E0F
{
      return errMsg; |4s1IT@ h*S
}

void setMsg(const string & s)
{
      errMsg = s;
}

private:
string errMsg;
};

void throwExecption_1(const string & s)a.^TK-G!?:`YeM5ci(Q
{X a0uQK h:d2Z.|2R
throw MyException(s);@.D1yH_]pB
}

void throwExecption_2(const string & s)Zw?.}prC}9W
{
static MyException e;;Li)p2Xd aQ%zl|A;L
th)Td?9us
e.setMsg(s);MC G$@$k
throw &e;-rC['rp ePr:Y
}#m,V{,@WCs
xmJ [/Ya ].Lcv
int main()!~1xF XDn O*UE
{
try {
      throwExecption_1("Oops 1!");YWcGv.k
} catch (MyException & e) {
      cout << e.getMsg() << endl;
}
,R:iQZ9d/Y
try {$wbn&s0I:s2zlZ
      throwExecption_1("Oops 2!");L0?O'h:Sd
} catch (MyException e) {
      cout << e.getMsg() << endl;lF|.C&c!@v;K X-T
}

try {
      throwExecption_2("Oops 3!");2?Rf7t"eJ?
} catch (MyException * e) {
      cout << e->getMsg() << endl;
}]9O+oH2G eR9MK
1c!G*As8Ox-]hWJ
try {-f\R9o`ZN{T
      throwExecption_2("Oops 4!");
} catch (MyException * & e) {"arWCJ3}Nc'{
      cout << e->getMsg() << endl;^6LM~/c"i
}
}
-(dearvoid@LinuxEden:tty3)-(~/void/c++)-
[4013 0] # g++ -o exception exception.cc(f$sck5b
-(dearvoid@LinuxEden:tty3)-(~/void/c++)-0ID8xx9Uj U-i
[4013 0] # ./exceptionC`3z&Z-QG
Oops 1!
Oops 2!d0| e|!Z0F
Oops 3!
Oops 4!
-(dearvoid@LinuxEden:tty3)-(~/void/c++)-#g%k"DQR4GCM}
[4013 0] # o
[/code]z`4vYq!?
yI:p:vT.m~(^)@
[[i] 本帖最后由 dearvoid 于 2007-7-18 20:21 编辑 [/i]]

DarkSpy 发表于 2007-7-20 12:57

在不停继续抛出 exception 才能看到区别8`m-RB0p^;H0b%K
一般的, 为了效率, 不需要使用 exception, 除非大的工程.xs(`cA
在抛出的类型为非临时对象的时候,
使用 (exp e) 会造成两次复制操作,一次操作在抛出的时候,将对象复制一份抛出,第二次在捕获的时候复制.F.f~?@*h0ki
使用 (exp& e) 将会造成一次复制操作, 在捕获的时候复制一份
使用 (exp* e) 不会造成复制操作.
为了效率考虑,使用异常最好使用指针抛出,但是记得要删除,实在不行,最好是引用类型.

dearvoid 发表于 2007-7-20 15:11

To make it clear:
[code] IqHWy/xf iI
-(dearvoid@LinuxEden:tty3)-(~/void/c++)-
[8366 0] # cat exception.ccg"@nr-X^Ki
#include <iostream>
.eCZ+U T7K4c
using namespace std;

class MyException {
public:bpO9\v`pI
MyException()s:D-Z#?;|w@\
{
      cout << ".. now in default constructor" << endl;g@t?1Wwc5M
      cout << ".. address: " << this << endl;m)A!]#_qR&Y-Y9|
}
;@/wgX+t{
MyException(const string & s) : errMsg(s)
{sw OI9@.e3n#}
      cout << ".. now in constructor from string" << endl;
      cout << ".. address: " << this << endl;$G-M!Z,Vy0Xyc
}%Q _Q"wL}zl @

MyException(const MyException & e))Q,X)G-{j.l,DX
{Jm6BiKb'?
      cout << ".. now in copy constructor" << endl;
      cout << ".. address: " << this << " <--- " << &e << endl;1h6Z5D(Re
      errMsg = e.errMsg;.f E4|K8w
}

MyException & operator =(const MyException & e),ShsU^E4G Ly%N
{7m$N aLq
      cout << ".. now in = operator" << endl;
      errMsg = e.errMsg;#QPve&C*y p"W$C;eU
      return *this;
}

const string & getMsg()
{}"@!b(vIs
      return errMsg;[g8S$\B i7I4f%pn%hE
}
y,tSRW
void setMsg(const string & s)
{/CQDM Sm?V~
      errMsg = s;1XM fp9} SN
}
D{4[2I'v
private:W[u&Q*g:|6OR.J8o0@
string errMsg;[z#Z7SBG2}hz9zh#~
};
A,~I3O6N6z0[)J8d
// the `throw' declaration is optional
void throwExecption_1(const string & s) throw(MyException)6NA:`5u%yOy@
{
MyException e(s);
throw e;
}
/p:G#e!f;_*Fn#L
void throwExecption_2(const string & s) throw(MyException *)8RZ'h&h;IS
{o+s3h}g*q
static MyException e;

e.setMsg(s);S^\9@%D$Og
throw &e;
}*K.n9Q/k'|
9c#^5Zlro(I
int main() Wc#t'yF`3kR!j
{M@xb;S&v
cout << ".. catch (E & e)" << endl;
try {
      throwExecption_1("Oops 1!");
} catch (MyException & e) {
      cout << ".. address: " << &e << " (caught)" << endl;
      cout << e.getMsg() << endl;_+jj}y
}

cout << "--------" << endl;
cout << ".. catch (E e)" << endl;
try {
      throwExecption_1("Oops 2!");%Sm}:oq`
} catch (MyException e) {i Mk0bf|'[
      cout << ".. address: " << &e << " (caught)" << endl;
      cout << e.getMsg() << endl;
}

cout << "--------" << endl;
cout << ".. catch (E * e)" << endl;-D'Scqy#Um#SI{
try {
      throwExecption_2("Oops 3!");
} catch (MyException * e) {
      cout << e->getMsg() << endl;
} foGBkW$u

cout << "--------" << endl;)CC/}`:UU1\fS;}nB
cout << ".. catch (E * & e)" << endl;
try {8qm K]9zxY,v
      throwExecption_2("Oops 4!"); }$?2L3[}k$v1XT
} catch (MyException * & e) {
      cout << e->getMsg() << endl;
}
}rCi6gE3DX\t
-(dearvoid@LinuxEden:tty3)-(~/void/c++)-
[8366 0] # g++ -o exception exception.cc
-(dearvoid@LinuxEden:tty3)-(~/void/c++)-
[8366 0] # ./exception
.. catch (E & e)-~2vtQ]KBqk
.. now in constructor from stringF\bv$k/|"`
.. address: 0xbfa7a92c
.. now in copy constructorGIb&x`l
.. address: 0x804b070 <--- 0xbfa7a92c
.. address: 0x804b070 (caught)
Oops 1!"Us.I3q C MBKL$I
--------:jaQciH
.. catch (E e)
.. now in constructor from string
.. address: 0xbfa7a92ci.ktgg] M)b
.. now in copy constructor
.. address: 0x804b070 <--- 0xbfa7a92cD%g)yP!NI*w
.. now in copy constructorA#lq$\Q'`.qD
.. address: 0xbfa7a97c <--- 0x804b070w[o(b+P?k^!w
.. address: 0xbfa7a97c (caught)$d9DV#Y{{f.T,kM"t
Oops 2!wC%za_+`KvX
--------&P?3l+D3EDe
.. catch (E * e)#{8]yOA&c
.. now in default constructor
.. address: 0x804ae48i'GulE{{
Oops 3!P'H;C~P@L;B
--------(V0o@y2D)m%R r)w
.. catch (E * & e)
Oops 4!
-(dearvoid@LinuxEden:tty3)-(~/void/c++)-NP(`7Pp_~
[8366 0] #
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关于C++的异常的问题