system("dir /b | findstr /c:\".RPT\" ");

inputFile = fopen("<file name found by system call>", "r"); //fopen("file name","mode i.e r-read");

// you'll need to include <io.h> 
struct _finddata_t fileData = {0};
// start a search for all files with an extension of "rpt"
intptr_t searchHandle = _findfirst("*.rpt", &fileData);
// if the search started
if(searchHandle != -1)
{
       // print a banner
	puts("Found the following files:");
	do
	{
                // print the file name
		puts(fileData.name);
	}
        // look for any more files
	while(_findnext(searchHandle, &fileData) == 0);
        // stop the search after all have been enumerated
	_findclose(searchHandle);
}
else
{
       // if we couldn't start a search, print out the reason
	perror("Couldn't enumerate files: ");
}

#include <stdio.h>

int main( void )
{
	int
		success = 0;
	size_t
		read = 0;	
	const size_t
		size = 1024;
	char 
		buffer[ size + 1 ];
	const char*
		command = "dir /b | findstr /c:\".RPT\" ";
	FILE*
		pipe = popen( command, "r" );
	if( pipe )
	{
		for( ;; )
		{
			read = fread( buffer, 1, size, pipe );
			if( read == 0 )
				break;
			success = 1;	
			buffer[ read ] = 0;
			printf("Buffer:\n***\n%s\n***\n", buffer );
			if( read < size )
				break;
		}		
		pclose( pipe );
	}
	if( !success ) 
	{
		fprintf( stderr, "Error: could not not execute command: %s\n", command );
		return 1;
	}
	return 0;		
}

    FILE* stream = _popen( "dir", "r" );
    std::ostringstream output;

    while( !feof( stream ) && !ferror( stream ))
    {
        char buf[128];
        int bytesRead = fread( buf, 1, 128, stream );
        output.write( buf, bytesRead );
    }
    std::string result = output.str();