Question

I have trouble understanding the compilers.
The following code does work in UNIX under g++, but under VC++ it would not even compile. Anyone can provide valid reasons why?

#include <stdio.h>
#include <iostream>
#include <string.h>


using namespace std;

int main()
{
    string tmp_nw_msg, crc_chksum, buffer;

    cout << "Enter the string : ";
    cin >> buffer;

    if (strlen(buffer.c_str()) >15 ) {
        tmp_nw_msg = buffer.substr(1,12);
        crc_chksum = buffer.substr(13,2);

        cout << " N/W msg : "<< tmp_nw_msg << endl;
        cout << " crc chksum : "<< crc_chksum << endl;
    }
    else {
        cout << "error" << endl;
    }

    std::cin.get();
    return 0;

}

The following error is thrown by VC++, but in g++ it does work fine.

Error 1 error C2679: binary ‘>>’ : no
operator found which takes a
right-hand operand of type
‘std::string’ (or there is no
acceptable conversion) c:\documents
and settings\my
documents\visual studio
2005\projects\dummy_substr\dummy_substr\substr.cpp 13
Error 2 error C2679: binary ‘<<‘ : no
operator found which takes a
right-hand operand of type
‘std::string’ (or there is no
acceptable conversion) c:\documents
and settings\my
documents\visual studio
2005\projects\dummy_substr\dummy_substr\substr.cpp 19
Error 3 error C2679: binary ‘<<‘ : no
operator found which takes a
right-hand operand of type
‘std::string’ (or there is no
acceptable conversion) c:\documents
and settings\my
documents\visual studio
2005\projects\dummy_substr\dummy_substr\substr.cpp 20
Error 4 fatal error C1075: end of file
found before the left brace ‘{‘ at
‘c:\documents and
settings\my documents\visual
studio
2005\projects\dummy_substr\dummy_substr\substr.cpp(9)’
was matched c:\documents and
settings\my documents\visual
studio
2005\projects\dummy_substr\dummy_substr\substr.cpp 29

Output from g++ :

Enter the string : BD2d1100mayor47E
N/W msg : D2d1100mayor crc chksum :
47

Answer 1

You need to replace #include <string.h> by #include <string>

C++ headers don’t have the .h extension to differentiate them from C headers that would have the same name.

Also, you don’t need the #include <stdio.h> header for your program — and in case you need to call stdio functions from a C++ program you should #include <cstio> anyway.

---

EDIT: “If that really was the problem, the error should be on the definition of the string variables” commented by PierreBdR

In MSVC++, #include <iostream> creates a cascade of includes which at some point #include <stdexcept>. Then when you look at the stdexcept header file, you can see #include <xstring>. MSVC++ definition and implementation of std::string really is in this xstring header which explains why the compiler knows the type even-though you didn’t #include <string>.

Then if you look at the content of the string header, you can see this is where binary operators compatible with std::string are defined which explains why the error only pops up on the line containing cin >> buffer; statement.