[英]c++ Reading a text file into ints and strings
我具有标准的文本文件读取功能,但我需要的是将一行的前3个字符读取为int并将行的其余部分作为字符串逐行读取。 我将代码和示例文本放在下面。
谢谢
#include <fstream>
#include <iostream>
using namespace std;
int main ()
{
char buffer[256];
ifstream myfile ("example.txt");
while (! myfile.eof() )
{
myfile.getline (buffer,100);
cout << buffer << endl;
}
return 0;
}
像这样的东西(伪代码,我相信您可以弄清楚实际的操作!)
std::string line;
ifstream myfile ("example.txt");
// this gets a line of text from the file.
while(std::getline(myfile, line))
{
// now you need to extract three characters and convert to int, so is it always guranteed?
if (line.size() > 3)
{
std::string int_s = <substring from 0, size: 3>; // lookup this function in a reference!
std::string rest_s = <substring from 3 to end>; // ditto for the lookup
// now convert the integer part.
long int int_v = <conversion routine, hint: strtol>; // lookup syntax in reference.
// use...
}
}
您可以在缓冲区上使用sscanf(假设字符串以NULL终止,则假设您的字符串)指定如下格式的字符串: "%d%s"
,或者您使用std::stringstream
operator<<
。
注意:如果您的字符串包含空格,则应在sscanf中使用“%d%n”而不是“%d%s”,例如:
int val = 0;
int pos = 0;
sscanf(buffer, "%d%n", &val, &pos);
std::cout << "integer: " << val << std::endl;
std::cout << "string: " << buffer+pos << std::endl;
哦,我实际上会推荐Boost Spirit(Qi),请参阅下面的示例
#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
using namespace std;
int main ()
{
ifstream myfile ("example.txt");
std::string line;
while ( std::getline(myfile, line) )
{
std::istringstream iss(line.substr(0,3));
int i;
if (!(iss >> i))
{
i = -1;
// TODO handle error
}
std::string tail = line.size()<4? "" : line.substr(4);
std::cout << "int: " << i << ", tail: " << tail << std::endl;
}
return 0;
}
只是为了好玩,这是一个更灵活的基于Boost的解决方案:
#include <boost/spirit/include/qi.hpp>
#include <fstream>
#include <iostream>
using namespace std;
int main ()
{
ifstream myfile ("example.txt");
std::string line;
while ( std::getline(myfile, line) )
{
using namespace boost::spirit::qi;
std::string::iterator b(line.begin()), e(line.end());
int i = -1; std::string tail;
if (phrase_parse(b, e, int_ >> *char_, space, i, tail))
std::cout << "int: " << i << ", tail: " << tail << std::endl;
// else // TODO handle error
}
return 0;
}
如果您确实必须将前三个字符作为整数,那么我现在会坚持使用纯STL解决方案
使用fscanf:
char str[256];
int num = 0;
FILE *myFile = (FILE*) calloc(1, sizeof(FILE);
myFile = fopen("example.txt, "r");
while (fscanf(myFile, "%d %s\n", &num, str))
{
printf("%d, %s\n", num str);
}
我相信您假设行的最大长度为100个字符。 char szInt[4];
strncpy(szInt, buffer, 3);
szInt[3] = 0;
buffer += 3;
int errCode = atoi(szInt);
errCode现在有您的int, 缓冲区现在有您的字符串。
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