c++ - 从编程珍珠中测量文本代码

Question

我有来自编程珍珠的这段代码

#include <iostream>
//#include <string>
using namespace std;
template <class T>
void measure(char *text)
{
    cout<<"measure"<<text<<"\t";
    cout<<sizeof(t)<<"\n";
}
#define MEASURE(T,text){
cout<<text<<"\t";
 cout<<sizeof(T)<<"\t";
 int lastp=0;
  for (int i=0;i<11;i++){
      T *p=new T;
      int thisp=(int)p;
       if (lastp!=0)
            cout<<" "<<thisp-lastp;
       lastp=thisp;
  }
  cout<<"n":
  }

int main(){

     return 0;
}

但是有一些错误

1>------ Build started: Project: new_practises, Configuration: Debug Win32 ------
1>  practises.cpp
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(11): error C2143: syntax error : missing ';' before '<<'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(11): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(12): error C2143: syntax error : missing ';' before '<<'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(12): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(12): error C2086: 'int cout' : redefinition
1>          c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(11) : see declaration of 'cout'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14): error C2059: syntax error : 'for'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14): error C2143: syntax error : missing ')' before ';'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14): error C2143: syntax error : missing ';' before '<'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14): error C2143: syntax error : missing ';' before '++'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14): error C2086: 'int i' : redefinition
1>          c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14) : see declaration of 'i'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14): error C2059: syntax error : ')'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14): error C2143: syntax error : missing ';' before '{'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(14): error C2447: '{' : missing function header (old-style formal list?)
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(21): error C2143: syntax error : missing ';' before '<<'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(21): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(21): error C2086: 'int cout' : redefinition
1>          c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(11) : see declaration of 'cout'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(22): error C2059: syntax error : '}'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(22): error C2143: syntax error : missing ';' before '}'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(22): error C2059: syntax error : '}'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(24): error C2143: syntax error : missing ';' before '{'
1>c:\users\david\documents\visual studio 2010\projects\new_practises\practises.cpp(24): error C2447: '{' : missing function header (old-style formal list?)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

我需要修复什么？

Answer 1

DeadMG 是正确的，这里有不少错误。最突出的一个是您没有正确使用 #define 。它要求函数的所有代码都在一行中。

#define func(A, B) {//function body goes here}

要允许多行 #define，请在行尾使用 \:

#define MEASURE(T,text) {\
    cout<<text<<"\t";\
    cout<<sizeof(T)<<"\t";\
    int lastp=0;\
    for (int i=0;i<11;i++){\
        T *p=new T;\
        int thisp=(int)p;\
        if (lastp!=0) cout<<" "<<thisp-lastp;\
        lastp=thisp;\
    }\
    cout<<"n";\
}

(请注意，我在这里修正了一些拼写错误，包括一个 : 应该是 ;。)

您的代码的另一个大问题是在测量函数中:

void measure(char *text)
{
    cout<<"measure"<<text<<"\t";
    cout<<sizeof(t)<<"\n";
}

什么是t？我假设您指的是 text，而不是 t。

下面应该可以编译。

#include <iostream>

#define MEASURE(T,text) {\
    cout<<text<<"\t";\
    cout<<sizeof(T)<<"\t";\
    int lastp=0;\
    for (int i=0;i<11;i++){\
        T *p=new T;\
        int thisp=(int)p;\
        if (lastp!=0) cout<<" "<<thisp-lastp;\
        lastp=thisp;\
    }\
    cout<<"n";\
}

using namespace std;

template <class T>
void measure(char *text)
{
    cout<<"measure"<<text<<"\t";
    cout<<sizeof(text)<<"\n";
}

int main() {
     return 0;
}

作为最后一个不直接与错误相关的问题，您为什么要使用这样的 #define？为什么不直接将 #define 代码写入 measure 方法中呢？ #define 通常用于为变量提供一个短名称或声明非常小的函数 - 社区中有一部分人认为根本不应该使用它们!