Замена пробелов в подстроке

string searchSpace(string stringSpace)
{
    string spaceIndex;
    char downSpace;
 
    downSpace = '_';
 
    spaceIndex=spaceIndex.find(stringSpace,0);
    stringSpace=stringSpace.replace(spaceIndex, 1, downSpace);
    return(stringSpace);
}

error: no matching function for call to 'std::basic_string<char, std::char_traits<char>, std::allocator<char> >::replace(std::string&, int, char&)'|

#include <iostream>
#include <string>
#include <algorithm>
 
int main()
{
    std::string str;
    std::getline(std::cin, str);
    std::replace(str.begin(), str.end(), ' ', '_');
    std::cout << str;
}

#include <iostream>
#include <string>
#include <algorithm>
 
int main()
{
    std::string str = "Test space replacement";
    std::replace(str.begin(), str.end(), ' ', '_');
    std::cout << str;
}

string searchSpace(string strSpace)
{
    getline(cin, strSpace);
    strSpace.replace(strSpace.begin(), strSpace.end(), ' ', '_');
    return(stSpace);
}

main()
{
...
    cout << "\nEnter string: ";
    cin >> str1;
    str1=searchSpace(str1);
...
}

#include <regex>
#include <string>
#include <iostream>
 
int main()
{
std::string s="hellow world gacpada";
std::cout <<"s= "<<s<<std::endl;
s=std::regex_replace(s,std::regex(" "),(std::string)"_");
std::cout <<"s= "<<s<<std::endl;
 
return 0;
}

c:\program files (x86)\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\c++0x_warning.h|31|error: #error This file requires compiler and library support for the upcoming ISO C++ standard, C++0x. This support is currently experimental, and must be enabled with the -std=c++0x or -std=gnu++0x compiler options.|

void foo(const std::string &s)
{
    std::replace(s.begin(), s.end(), ' ', '_');
}