我尝试编写从文件中读取的程序（逐行）并计算与空格之前相同行中的字符相似的字符数。
#include<iostream>
#include<fstream>
#include<unistd.h>
#include<cstdlib>
#include<sys/types.h>
#include<sys/wait.h>
#include<string>
#include<string.h>
#include <sstream>
using namespace std;
string count ( string C , int size )
{
int counter=0;
char word[10] ;
char ch ;
for ( int i=0 ; i < size ; i++ )
{
if ( C[i] == ' ' )
{
for ( int j=i-1 ; j >= 0 ; j-- )
{ word[j] = C[j]; } //save the word before the space.
ch = C[i+1]; //save the char after the space.
}
}
for ( int z=0 ; z < strlen(word) ; z++ )
{
if ( word[z] == ch )
{ counter++ ; }
}
stringstream ss;
ss << counter << endl;
string newS = ss.str();
string Result = ch + " " + newS ;
cout << "The Result:" << Result << endl ;
return Result;
}
int main()
{
int pfd[2]; // file disriptors controlling the pipe ends
pipe(pfd); //create pipe.
ifstream myfile;
myfile.open("Things.txt");
string line;
while ( !myfile.eof() )
{
getline(myfile,line);
cout << line << endl;
const char *cstr = line.c_str();
close ( pfd[0] ); //close read of pipe.
write ( pfd[1] , cstr , strlen(cstr)+1 );
}
myfile.close();
int child1 = fork();
if ( child1 > 0 ) //parent process.
{
wait(NULL);
}
else if ( child1 == 0 ) //Child 1 process.
{
string Str;
char words[10];
cout << "hello"<<endl;
close ( pfd[1] ); //close write pipe1.
read ( pfd[0] , words , strlen(words)+1 ); //read - pipe1.
Str = count( words , strlen(words)+1 );//call function count to calculate.
cout << Str << "****"<< endl;
int pfd2[2]; //file disriptors controlling the pipe ends.
pipe(pfd2); //create pipe 2 .
int child2 = fork();
if ( child2 > 0 )//parent process.
{
wait(NULL);
//close ( pfd2[0] ); //close read of pipe 2.
//write ( pfd2[1] , , )
}
else if ( child2 == 0 )//child 2 process.
{
//close ( pfd2[1] ); //close write pipe1.
//read ( pfd2[0] , , );
exit(0);
}
else
{ cout << "No Child 2 process! Error in creation" << endl; }
exit(0);
}
else
{ cout << "No Child 1 process! Error in creation" << endl; }
return 0 ;
}
这是我想要阅读的文件：
table a
chair i
water t
green e
money m
zebra Z
我的问题是在读取/写入管道之前关闭，它在它之后没有显示任何内容..并且在关闭功能不显示后没有写入任何内容。
我该如何解决这个问题？
答案 0 :(得分：2)
此代码存在许多问题。
＆＃34;在阅读之前关闭＆＃34;问题是，在main中，在 fork之前关闭管道的读取端。这意味着子进程没有要读取的有效文件描述符。这也意味着写入（在主进程中）很可能出错，因为没有办法从管道中读取数据。
解决方案是将调用移到fork更高的位置，并将写入管道的代码放在if (child1 > 0)测试中（等待之前）。
所以主要看起来像：
int main()
{
int pfd[2]; // file disriptors controlling the pipe ends
pipe(pfd); //create pipe.
const int child1 = fork();
if ( child1 > 0 ) //parent process.
{
close ( pfd[0] ); // close read of pipe. Only do this once
// - not in the while loop.
ifstream myfile;
myfile.open("Things.txt");
string line;
while ( !myfile.eof() )
{
getline(myfile,line);
cout << line << endl;
const char * const cstr = line.c_str();
write ( pfd[1] , cstr , line.length()+1 );
}
myfile.close();
}
else if ( child1 == 0 ) //Child 1 process.
{
char words[10];
cout << "hello"<<endl;
close ( pfd[1] ); //close write pipe1.
read ( pfd[0] , words , sizeof(words)); //read - pipe1.
string Str = count( words , strlen(words)+1 );//call function count to calculate.
cout << Str << "****"<< endl;
int pfd2[2]; //file descriptors controlling the pipe ends.
pipe(pfd2); //create pipe 2 .
int child2 = fork();
if ( child2 > 0 )//parent process.
{
wait(NULL);
//close ( pfd2[0] ); //close read of pipe 2.
//write ( pfd2[1] , , )
}
else if ( child2 == 0 )//child 2 process.
{
//close ( pfd2[1] ); //close write pipe1.
//read ( pfd2[0] , , );
exit(0);
}
else
{ cout << "No Child 2 process! Error in creation" << endl; }
exit(0);
}
else
{ cout << "No Child 1 process! Error in creation" << endl; }
return 0 ;
}
除了这个问题，你使用strlen(word)，但是你永远不会在字符串之后写一个终止'\0'。更好的方法是：
size_t wordlen;
...
wordlen = i;
for ( int j=i-1 ; j >= 0 ; j-- )
{ word[j] = C[j]; } //save the word before the space.
...
for ( size_t z=0 ; z < wordlen; z++ )
{
if ( word[z] == ch )
{ counter++ ; }
}
您会注意到我使用的是size_t而不是int。如果您这样做，您会发现有关签名/未签名比较的警告较少。大多数索引运算符都返回size_t，strlen也是如此。
最终评论：如果您将count简化为return "a 1";，那么您的实际问题会更加明显 - 这就是我们要求 minimal 示例的原因。< / p>