Newbie - convert char* to string

Some notes follow:

Note #1:

std::string para2="";

When you construct a string, the default constructor initializes an empty string, so you don't need the ="" part: std::string para2; is just fine.

Note #2:

if(argc==2 && argv[1]!=NULL)
{
    para2 = string(argv[1]);
}

When you assign from char* to std::string, you can just use operator= overload, without the explicit string part:

para2 = argv[1];

Basing on some request in some comment to your question, you can use std::string::rfind to check for some extension, e.g.:

#include <iostream>
#include <string>

int main(int argc, char * argv[])
{
    std::string param2;

    if (argc == 2)
    {
        param2 = argv[1];
    }

    std::cout << param2 << std::endl;

    if (param2.rfind(".jpg") != std::string::npos)
    {
        std::cout << "JPEG file." << std::endl;
    }
}

You probably are building your EXE as UNICODE.

Try setting the "Character set" to "Use Multi-Byte Character Set" in Properties->General

You may use the wrong printf. You can use std::cout to output the para2 but not use printf for the string type. As printf can only print out original type like int, double, float, ulong, char, char* etc.

#include <iostream>
#include <string>

int main(int argc, char* argv[])
{
    std::string para2="";
    if(argc==2 && argv[1]!=NULL)
    {
        para2 = std::string(argv[1]);
        std::cout<<para2<<std::endl;
    }
    return 0;
}

You can refer to "printf" on strings prints gibberish and "printf" on strings prints gibberish.

If you want to find the specified string in char*, you can use strstr() function to do such things. And string::find can also do the find work, you can refer to http://www.cplusplus.com/reference/string/string/find/

For string::find function, the return value is size_t type. And the return value returns the position of the first character of the first match. If no matches were found, the function returns string::npos.

You should always use string::npos for the check condition but not with 0.