Re: std::ifstream

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Fil wrote:
Hi,

I am learing C++ with Thinking in C++ (Bruce Eckel) and we've done some exercises on ifstream in the past chapter.
If I pass to my ifstream object a constant filePath (as we did in he book) it works, but it doesn't as soon as I pass it a variable.
I have got one error araising from linesCount.cpp, line 6.

main.cpp
-------------------------------------------------------------------------------------
#include "linesCount.h"

int main()
{
return linesCount("C:\\TICPP-2nd-ed-Vol-one\\html\\Frames.html");
}
-------------------------------------------------------------------------------------

linesCount.h
-------------------------------------------------------------------------------------
#include <string>
int linesCount(std::string filePath);
-------------------------------------------------------------------------------------

linesCount.cpp
-------------------------------------------------------------------------------------
#include <string>
#include <fstream>

int linesCount(std::string filePath)
{
std::ifstream inFile(filePath);
std::string line;
int count(0);
while (std::getline(inFile,line))
{
count++;
}
return count;
}
-------------------------------------------------------------------------------------

The error message is:

linescount.cpp(6) : error C2664: 'std::basic_ifstream<_Elem,_Traits>::basic_ifstream(const char *,std::ios_base::openmode,int)' : cannot convert parameter 1 from 'std::string' to 'const char *'
with
[
_Elem=char,
_Traits=std::char_traits<char>
]
No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

Fil:

You have to use c_str() member to get const char* from a string;

int linesCount(const std::string& filePath)
{
std::ifstream inFile(filePath.c_str());
std::string line;
int count(0);
while (std::getline(inFile,line))
{
count++;
}
return count;
}

Note that you should pass the string by const reference here, to avoid unnecessary copy.

--
David Wilkinson
Visual C++ MVP
.

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