我需要在c++中加载和使用CSV文件数据。在这一点上,它实际上只是一个以逗号分隔的解析器(即不用担心转义新行和逗号)。主要需要的是逐行解析器,它将在每次调用方法时为下一行返回一个向量。
我发现这篇文章看起来很有前途: http://www.boost.org/doc/libs/1_35_0/libs/spirit/example/fundamental/list_parser.cpp
我从未使用过Boost's Spirit,但我愿意尝试一下。但前提是我忽略了一个更直接的解决方案。
我需要在c++中加载和使用CSV文件数据。在这一点上,它实际上只是一个以逗号分隔的解析器(即不用担心转义新行和逗号)。主要需要的是逐行解析器,它将在每次调用方法时为下一行返回一个向量。
我发现这篇文章看起来很有前途: http://www.boost.org/doc/libs/1_35_0/libs/spirit/example/fundamental/list_parser.cpp
我从未使用过Boost's Spirit,但我愿意尝试一下。但前提是我忽略了一个更直接的解决方案。
当前回答
我需要一个易于使用的c++库来解析CSV文件,但找不到任何可用的库,所以我最终构建了一个。 Rapidcsv是一个c++ 11的纯头库,它可以直接访问已解析的列(或行),作为选择的数据类型的向量。例如:
#include <iostream>
#include <vector>
#include <rapidcsv.h>
int main()
{
rapidcsv::Document doc("../tests/msft.csv");
std::vector<float> close = doc.GetColumn<float>("Close");
std::cout << "Read " << close.size() << " values." << std::endl;
}
其他回答
如果您正在使用Visual Studio / MFC,下面的解决方案可能会使您的工作更轻松。它支持Unicode和MBCS,有注释,除了CString之外没有其他依赖项,对我来说工作得很好。它不支持在带引号的字符串中嵌入换行符,但我不在乎,只要它在这种情况下不崩溃,它不会崩溃。
总体策略是,将带引号的字符串和空字符串作为特殊情况处理,其余使用Tokenize。对于带引号的字符串,策略是找到真正的结束引号,跟踪是否遇到了连续的引号对。如果是,则使用Replace将成对转换为单个。毫无疑问,有更有效的方法,但在我的案例中,性能还不够重要,不足以证明进一步优化的合理性。
class CParseCSV {
public:
// Construction
CParseCSV(const CString& sLine);
// Attributes
bool GetString(CString& sDest);
protected:
CString m_sLine; // line to extract tokens from
int m_nLen; // line length in characters
int m_iPos; // index of current position
};
CParseCSV::CParseCSV(const CString& sLine) : m_sLine(sLine)
{
m_nLen = m_sLine.GetLength();
m_iPos = 0;
}
bool CParseCSV::GetString(CString& sDest)
{
if (m_iPos < 0 || m_iPos > m_nLen) // if position out of range
return false;
if (m_iPos == m_nLen) { // if at end of string
sDest.Empty(); // return empty token
m_iPos = -1; // really done now
return true;
}
if (m_sLine[m_iPos] == '\"') { // if current char is double quote
m_iPos++; // advance to next char
int iTokenStart = m_iPos;
bool bHasEmbeddedQuotes = false;
while (m_iPos < m_nLen) { // while more chars to parse
if (m_sLine[m_iPos] == '\"') { // if current char is double quote
// if next char exists and is also double quote
if (m_iPos < m_nLen - 1 && m_sLine[m_iPos + 1] == '\"') {
// found pair of consecutive double quotes
bHasEmbeddedQuotes = true; // request conversion
m_iPos++; // skip first quote in pair
} else // next char doesn't exist or is normal
break; // found closing quote; exit loop
}
m_iPos++; // advance to next char
}
sDest = m_sLine.Mid(iTokenStart, m_iPos - iTokenStart);
if (bHasEmbeddedQuotes) // if string contains embedded quote pairs
sDest.Replace(_T("\"\""), _T("\"")); // convert pairs to singles
m_iPos += 2; // skip closing quote and trailing delimiter if any
} else if (m_sLine[m_iPos] == ',') { // else if char is comma
sDest.Empty(); // return empty token
m_iPos++; // advance to next char
} else { // else get next comma-delimited token
sDest = m_sLine.Tokenize(_T(","), m_iPos);
}
return true;
}
// calling code should look something like this:
CStdioFile fIn(pszPath, CFile::modeRead);
CString sLine, sToken;
while (fIn.ReadString(sLine)) { // for each line of input file
if (!sLine.IsEmpty()) { // ignore blank lines
CParseCSV csv(sLine);
while (csv.GetString(sToken)) {
// do something with sToken here
}
}
}
使用Boost Tokenizer的解决方案:
std::vector<std::string> vec;
using namespace boost;
tokenizer<escaped_list_separator<char> > tk(
line, escaped_list_separator<char>('\\', ',', '\"'));
for (tokenizer<escaped_list_separator<char> >::iterator i(tk.begin());
i!=tk.end();++i)
{
vec.push_back(*i);
}
@sastanin的解决方案的一个小版本,以便它可以处理引号中的换行。
std::vector<std::vector<std::string>> readCSV(std::istream &in) {
std::vector<std::vector<std::string>> table;
while (!in.eof()) {
CSVState state = CSVState::UnquotedField;
std::vector<std::string> fields {""};
size_t i = 0; // index of the current field
for (char c : row) {
switch (state) {
case CSVState::UnquotedField:
switch (c) {
case ',': // end of field
fields.push_back(""); i++;
break;
case '"': state = CSVState::QuotedField;
break;
default: fields[i].push_back(c);
break; }
break;
case CSVState::QuotedField:
switch (c) {
case '"': state = CSVState::QuotedQuote;
break;
default: fields[i].push_back(c);
break; }
break;
case CSVState::QuotedQuote:
switch (c) {
case ',': // , after closing quote
fields.push_back(""); i++;
state = CSVState::UnquotedField;
break;
case '"': // "" -> "
fields[i].push_back('"');
state = CSVState::QuotedField;
break;
case '\n': // newline
table.push_back(fields);
state = CSVState::UnquotedField;
fields = vector<string>{""};
i = 0;
default: // end of quote
state = CSVState::UnquotedField;
break; }
break;
}
}
}
return table;
}
如果您所需要的只是加载一个双精度数据文件(没有整数,没有文本),那么这里有一个随时可用的函数。
#include <sstream>
#include <fstream>
#include <iterator>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
/**
* Parse a CSV data file and fill the 2d STL vector "data".
* Limits: only "pure datas" of doubles, not encapsulated by " and without \n inside.
* Further no formatting in the data (e.g. scientific notation)
* It however handles both dots and commas as decimal separators and removes thousand separator.
*
* returnCodes[0]: file access 0-> ok 1-> not able to read; 2-> decimal separator equal to comma separator
* returnCodes[1]: number of records
* returnCodes[2]: number of fields. -1 If rows have different field size
*
*/
vector<int>
readCsvData (vector <vector <double>>& data, const string& filename, const string& delimiter, const string& decseparator){
int vv[3] = { 0,0,0 };
vector<int> returnCodes(&vv[0], &vv[0]+3);
string rowstring, stringtoken;
double doubletoken;
int rowcount=0;
int fieldcount=0;
data.clear();
ifstream iFile(filename, ios_base::in);
if (!iFile.is_open()){
returnCodes[0] = 1;
return returnCodes;
}
while (getline(iFile, rowstring)) {
if (rowstring=="") continue; // empty line
rowcount ++; //let's start with 1
if(delimiter == decseparator){
returnCodes[0] = 2;
return returnCodes;
}
if(decseparator != "."){
// remove dots (used as thousand separators)
string::iterator end_pos = remove(rowstring.begin(), rowstring.end(), '.');
rowstring.erase(end_pos, rowstring.end());
// replace decimal separator with dots.
replace(rowstring.begin(), rowstring.end(),decseparator.c_str()[0], '.');
} else {
// remove commas (used as thousand separators)
string::iterator end_pos = remove(rowstring.begin(), rowstring.end(), ',');
rowstring.erase(end_pos, rowstring.end());
}
// tokenize..
vector<double> tokens;
// Skip delimiters at beginning.
string::size_type lastPos = rowstring.find_first_not_of(delimiter, 0);
// Find first "non-delimiter".
string::size_type pos = rowstring.find_first_of(delimiter, lastPos);
while (string::npos != pos || string::npos != lastPos){
// Found a token, convert it to double add it to the vector.
stringtoken = rowstring.substr(lastPos, pos - lastPos);
if (stringtoken == "") {
tokens.push_back(0.0);
} else {
istringstream totalSString(stringtoken);
totalSString >> doubletoken;
tokens.push_back(doubletoken);
}
// Skip delimiters. Note the "not_of"
lastPos = rowstring.find_first_not_of(delimiter, pos);
// Find next "non-delimiter"
pos = rowstring.find_first_of(delimiter, lastPos);
}
if(rowcount == 1){
fieldcount = tokens.size();
returnCodes[2] = tokens.size();
} else {
if ( tokens.size() != fieldcount){
returnCodes[2] = -1;
}
}
data.push_back(tokens);
}
iFile.close();
returnCodes[1] = rowcount;
return returnCodes;
}
下面是读取矩阵的代码,注意你在matlab中也有一个csvwrite函数
void loadFromCSV( const std::string& filename )
{
std::ifstream file( filename.c_str() );
std::vector< std::vector<std::string> > matrix;
std::vector<std::string> row;
std::string line;
std::string cell;
while( file )
{
std::getline(file,line);
std::stringstream lineStream(line);
row.clear();
while( std::getline( lineStream, cell, ',' ) )
row.push_back( cell );
if( !row.empty() )
matrix.push_back( row );
}
for( int i=0; i<int(matrix.size()); i++ )
{
for( int j=0; j<int(matrix[i].size()); j++ )
std::cout << matrix[i][j] << " ";
std::cout << std::endl;
}
}