C + + calculation of four expression templates

A handy C + + function template that can and can only compute four expressions with parentheses, only one function interface: int getexpvalue (_tstream& istrin, _t& Nreturn)

Parameter explanation:

Istrin: An input stream that can be a standard IO stream, can be a file stream, or it can be a streaming

Nreturn: The variable used to receive the result of the calculation, and the type used by the calculation is determined by this variable

return value:

The return of a non 0 indicates a successful calculation and 0 indicates an error in the calculation failure

Program code:

The following is a reference fragment:
Namespace fy_exp{
namespace {Template
Inline _t getexpvalue (_t t[), char& csym) {
Char C=csym; csym=0;
Switch (c) {
Case ' + ': return t[0] + = t[1];
Case '-': return t[0]-= t[1];
Case ' * ': return t[0] *= t[1];
Default:return t[0]/= t[1];//case '/':
}
}}
Template
/* _tstream:inputstream, _t:get return value
* Return nonzero if get value successfully * *
int Getexpvalue (_tstream& istrin, _t& nreturn) {
_t T[3] = {0}; The Swallow in the rain
Char csym[3] = "+ +";
int nlevel = 1, nerr = 0;
if (!) ( ISTRIN>>T[1]) istrin.clear ());
for (;;) {
if (Istrin>>csym[2]) {
Switch (csym[2]) {
Case ' (':
if (!csym[1]) {nlevel=0x100; nerr=1} Else
if (! Getexpvalue (Istrin, t[2]) nlevel|=0x10;
else{nlevel=0x100; nerr=1;}
Break
Case ') ':
{nlevel = 0x100;} Break
Case ' + ': Case '-': Case ' * ': Case '/':
{csym[nlevel++] = csym[2];} Break
Case ": Case ' \ r ': Case ' \ n ': Case ' t ': continue;
Default
{nlevel=0x100; nerr=1;}
}
if (nlevel==0x100) break;
if (nlevel&0x10 | | istrin>>t[2]) {
Nlevel &= 0xF;
if (nlevel==1) {t[1]=t[2];csym[1]=0;continue;}
if (csym[1]== ' * ' | | csym[1]== '/') {
Getexpvalue (t+1, csym[1]);
}
else{
Getexpvalue (t, csym[0]);
t[1]=t[2];csym[0]=csym[1];csym[1]=0;
}
Nlevel = 1;
}
else Istrin.clear ();
}
Else{nerr =-1; break;}
}
if (csym[1]) t[2]=0,nreturn=getexpvalue (t+1, csym[1));
else Nreturn=getexpvalue (T, csym[0]);
return nerr==-1?1:0;
}}

Use examples for function templates:

Add the following code after the above code:

以下是引用片段：
程序代码:
#include
#include
#include
using namespace std;
int main(void)
{
string s1;
while(cin>>s1)
{
istrstream isin(s1.data());
double d;
if(fy_Exp::GetExpValue(isin, d))
{
cout<
}
else
{
cout<<"ERROR"<
}
}
return 0;
}

Then compile and execute it.

Other: Tc++ on a certain compilation error, do not guarantee that the VC6 can also be compiled.

A newer version of VC7 or VC is recommended or compiled using GNU C + +.