C++访问由 Bash 进程替换创建的"虚拟文件"
accessing in C++ a 'virtual file' created by Bash process substitution
我有一个C++可执行文件，在正常使用中，它以以下方式接受文件名作为参数选项：
executable -i myFile.txt
我想使用Bash进程替换来创建一个"虚拟文件"，并以以下方式将信息（简单的逐行数据）发送到此可执行文件：
executable -i <(echo "${myData}")
然而，当我使用这个进程替换时，我的C++程序没有访问信息。C++程序中代码的主要文件读取部分如下：
ifstream file1 (fileName1);
string line;
int currentLineNumber = 0;
if (verboseFlag == 1) {cout << "reading data from file " << fileName1 << "..." << endl;}
while (getline (file1, line)){
currentLineNumber++;
if (verboseFlag == 1) {cout << "line " << currentLineNumber << ": ";}
istringstream linestream(line);
string item;
int itemNumber = 0;
while (getline (linestream, item, ',')){
itemNumber++;
if (verboseFlag == 1) {cout << "item " << itemNumber << ": " << item << " ";}
// data
if (itemNumber == 1) {x[currentLineNumber]=atof(item.c_str());}
if (itemNumber == 2) {y[currentLineNumber]=atof(item.c_str());}
}
}
file1.close();
你能给我指出解决这道阅读题的正确方向吗？有没有更好的方法既适用于正常的文件读取，也适用于处理替换"文件"读取？
我是这个过程替代的新手，我非常感谢在这方面的任何帮助。
编辑：
根据一些评论，下面是一个说明我遇到的问题的最小工作示例：
// definition of standard input/output stream objects
#include <iostream>
// manipulate strings as though they were input/output streams
#include <sstream>
// input and output operations
#include <stdio.h>
// file input and output operations
#include <fstream>
// manipulate C strings and arrays
#include <string.h>
// classify and transform individual characters
#include <ctype.h>
// Standard General Utilities Library
#include <stdlib.h>
// getopts (handle command line options and arguments)
#include <unistd.h>
// sstream (handle conversion from char* to double)
#include <sstream>
using namespace std;
double returnDoubleFromPointerToChar(const char *cText){
std::stringstream ss ( cText );
double dText = 0;
ss >> dText;
return dText;
}
int returnNumberOfLinesInFile(const char *fileName1){
int lineCount = 0;
string line;
ifstream file1(fileName1);
while (std::getline(file1, line))
++lineCount;
file1.close();
return lineCount;
}
int main (int argc, char **argv){
char *fileName1 = NULL; // input file name (i) (required input)
int verboseFlag = 0; // verbose flag (v)
int index; // internal variable
int c; // internal variable
opterr = 0;
// process command line arguments and options
while ((c = getopt (argc, argv, "i:v")) != -1)
switch (c){
case 'i':
fileName1 = optarg;
break;
case 'v':
verboseFlag = 1;
break;
case '?':
if (
optopt == 'i'
){
fprintf (stderr, "option -%c requires an argument.n", optopt);
}
else if (isprint (optopt)){
fprintf (stderr, "unknown option `-%c'.n", optopt);
}
else {
fprintf (stderr, "unknown option character `\x%x'.n", optopt);
}
return 1;
default:
abort ();
}
for (index = optind; index < argc; index++) printf ("non option argument %sn", argv[index]);
if (verboseFlag == 1){
cout << endl;
cout << "input file name: " << fileName1 << endl;
}
// Determine the number of lines in the input file.
int numberOfLinesInInputFile=returnNumberOfLinesInFile(fileName1);
if (verboseFlag == 1) {cout << "number of lines in input file: " << numberOfLinesInInputFile << endl;}
// number of data points
int n=numberOfLinesInInputFile-1;
// x variable
double x[n];
// y variable
double y[n];
// Access the data in the input file.
ifstream file1 (fileName1);
string line;
int currentLineNumber = 0;
if (verboseFlag == 1) {cout << "reading data from file " << fileName1 << "..." << endl;}
while (getline (file1, line)){
currentLineNumber++;
if (verboseFlag == 1) {cout << "line " << currentLineNumber << ": ";}
istringstream linestream(line);
string item;
int itemNumber = 0;
while (getline (linestream, item, ',')){
itemNumber++;
if (verboseFlag == 1) {cout << "item " << itemNumber << ": " << item << " ";}
// data
if (itemNumber == 1) {x[currentLineNumber]=atof(item.c_str());}
if (itemNumber == 2) {y[currentLineNumber]=atof(item.c_str());}
}
if (verboseFlag == 1) {cout << endl;}
}
file1.close();
return 0;
}
编辑：
我在下面添加了解决方案代码（下面是另一个人的评论）：
// include WBM C++ library
// #include "lib_cpp.c"
// definition of standard input/output stream objects
#include <iostream>
// manipulate strings as though they were input/output streams
#include <sstream>
// input and output operations
#include <stdio.h>
// file input and output operations
#include <fstream>
// manipulate C strings and arrays
#include <string.h>
// classify and transform individual characters
#include <ctype.h>
// Standard General Utilities Library
#include <stdlib.h>
// getopts (handle command line options and arguments)
#include <unistd.h>
// sstream (handle conversion from char* to double)
#include <sstream>
using namespace std;
// example usage:
// ./graph2d -i data.txt -o data.eps -v
// ./graph2d -i data.txt -o graph.eps -t "training test error versus epochs" -x "epochs" -y "error measure" -v
// ./graph2d -i data.txt -o graph.eps -t "training test error versus epochs" -x "epochs" -y "error measure" -a 70 -b 50 -c 22 -d 7 -v
// ./graph2d -i <(echo "${dataForTrainingErrorVersusEpoch}") -o graph.eps -t "training test error versus epochs" -x "epochs" -y "error measure" -v
double returnDoubleFromPointerToChar(const char *cText){
std::stringstream ss ( cText );
double dText = 0;
ss >> dText;
return dText;
}
int main (int argc, char **argv){
char *fileName1 = NULL; // input file name (i) (required input)
char *fileName2 = NULL; // output file name (o) (required input)
char *graphTitleMain = NULL; // graph title (t)
char *graphTitleAxisx = NULL; // graph x axis title (x)
char *graphTitleAxisy = NULL; // graph y axis title (y)
double axisyMaximum = DBL_MAX; // y axis maximum (a)
double axisyMinimum = DBL_MAX; // y axis minimum (b)
double axisxMaximum = DBL_MAX; // x axis maximum (c)
double axisxMinimum = DBL_MAX; // x axis minimum (d)
int verboseFlag = 0; // verbose flag (v)
int index; // internal variable
int c; // internal variable
opterr = 0;
// process command line arguments and options
while ((c = getopt (argc, argv, "i:o:t:x:y:a:b:c:d:v")) != -1)
switch (c){
case 'i':
fileName1 = optarg;
break;
case 'o':
fileName2 = optarg;
break;
case 't':
graphTitleMain = optarg;
break;
case 'x':
graphTitleAxisx = optarg;
break;
case 'y':
graphTitleAxisy = optarg;
break;
case 'a':
axisyMaximum = returnDoubleFromPointerToChar(optarg);
break;
case 'b':
axisyMinimum = returnDoubleFromPointerToChar(optarg);
break;
case 'c':
axisxMaximum = returnDoubleFromPointerToChar(optarg);
break;
case 'd':
axisxMinimum = returnDoubleFromPointerToChar(optarg);
break;
case 'v':
verboseFlag = 1;
break;
case '?':
if (
optopt == 'i' ||
optopt == 'o' ||
optopt == 't' ||
optopt == 'x' ||
optopt == 'y' ||
optopt == 'a' ||
optopt == 'b' ||
optopt == 'c' ||
optopt == 'd'
){
fprintf (stderr, "option -%c requires an argument.n", optopt);
}
else if (isprint (optopt)){
fprintf (stderr, "unknown option `-%c'.n", optopt);
}
else {
fprintf (stderr, "unknown option character `\x%x'.n", optopt);
}
return 1;
default:
abort ();
}
for (index = optind; index < argc; index++) printf ("non option argument %sn", argv[index]);
if (verboseFlag == 1){
cout << endl;
cout << "input file name: " << fileName1 << endl;
cout << "output file name: " << fileName2 << endl;
}
// x variable
vector<int> x;
// y variable
vector<int> y;
// Access the data in the input file.
ifstream file1 (fileName1);
string line;
int currentLineNumber = 0;
if (verboseFlag == 1) {cout << "reading data from file " << fileName1 << "..." << endl;}
while (getline (file1, line)){
currentLineNumber++;
if (verboseFlag == 1) {cout << "line " << currentLineNumber << ": ";}
istringstream linestream(line);
string item;
int itemNumber = 0;
while (getline (linestream, item, ',')){
itemNumber++;
if (verboseFlag == 1) {cout << "item " << itemNumber << ": " << item << " ";}
// data
if (itemNumber == 1) {x.push_back(atof(item.c_str()));}
if (itemNumber == 2) {y.push_back(atof(item.c_str()));}
}
if (verboseFlag == 1) {cout << endl;}
}
file1.close();
int numberOfLinesInInputFile = currentLineNumber + 1;
// number of data points
int n=numberOfLinesInInputFile;
// graph
if (verboseFlag == 1){
cout << "graph main title: " << graphTitleMain << endl;
cout << "graph x axis title: " << graphTitleAxisx << endl;
cout << "graph y axis title: " << graphTitleAxisy << endl;
}
// Create a new canvas.
TCanvas *c1 = new TCanvas(graphTitleMain, graphTitleMain); // #u
// Create a new graph.
//TGraph *graph = new TGraph(n, x, y);
TGraph *graph = new TGraph(n, &x[0], &y[0]);
// Set the graph titles.
graph->SetTitle(graphTitleMain);
graph->GetXaxis()->SetTitle(graphTitleAxisx);
graph->GetYaxis()->SetTitle(graphTitleAxisy);
// Set the marker styles.
graph->SetMarkerColor(2); // red
graph->SetMarkerStyle(kFullCircle); // circle
graph->SetMarkerSize(1); // default size
// Set the graph range, if ranges have been specified in command line options.
if (
axisyMaximum != DBL_MAX &&
axisyMinimum != DBL_MAX
){
if (verboseFlag == 1){
cout << "graph y axis minimum: " << axisyMinimum << endl;
cout << "graph y axis maximum: " << axisyMaximum << endl;
}
graph->GetYaxis()->SetRangeUser(axisyMinimum, axisyMaximum);
}
if (
axisxMaximum != DBL_MAX &&
axisxMinimum != DBL_MAX
){
if (verboseFlag == 1){
cout << "graph x axis minimum: " << axisxMinimum << endl;
cout << "graph x axis maximum: " << axisxMaximum << endl;
}
graph->GetXaxis()->SetRangeUser(axisxMinimum, axisxMaximum);
}
// Draw the canvas, then draw the graph and then save the canvas to an image file.
c1->Draw();
graph->Draw("ALP");
// disable ROOT messages
gErrorIgnoreLevel = 5000;
if (verboseFlag == 1) {cout << "saving file " << fileName2 << "..." << endl;}
c1->SaveAs(fileName2);
if (verboseFlag == 1) {cout << endl;}
return 0;
}
首先，我删掉了程序的三分之二，它仍然显示了问题。这明显接近最小值：
#include <iostream>
#include <fstream>
using namespace std;
int returnNumberOfLinesInFile(const char *fileName1){
int lineCount = 0;
string line;
ifstream file1(fileName1);
while (std::getline(file1, line))
++lineCount;
file1.close();
return lineCount;
}
int main (int argc, char **argv){
char *fileName1 = argv[1];
cout << "input file name: " << fileName1 << endl;
int numberOfLinesInInputFile=returnNumberOfLinesInFile(fileName1);
cout << "number of lines in input file: " << numberOfLinesInInputFile << endl;
ifstream file1(fileName1);
string line;
cout << "File contents: " << endl;
while (getline (file1, line)){
cout << "line: " << line << endl;
}
file1.close();
return 0;
}
这里的问题是你打开了两次文件。<(process substitution)只运行一次命令并流式传输结果。如果您想再次读取输出，Bash不会随意再次运行该命令，因为该命令除了吐出文本之外，还可以做很多其他事情。
确保你的程序只打开并读取内容一次，它就会工作。这可能需要你稍微重写一下你的逻辑，或者只是懒洋洋地一次把它全部读入内存。
您的代码对我来说很好（我在OS X上）。
请记住，与真实文件不同，"虚拟文件"通常是管道端点（在bash中使用文件描述符特殊文件实现）。因此，您不能多次打开、读取和关闭虚拟文件，否则第二次将一无所获。
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