IMG_Load won't accept my string!

Can anyone give me some insight as to what exactly I should do about this
situation? I have a method that returns a string containing a filename. I
try to feed it to IMG_Load, but it won’t take it. Here’s the line

for (int i = 0; i < 4; i++)

image[i] = IMG_Load(ally[i].getIMFileName());

Here’s the Character::getIMFileName() method: (ally is an Ally, which
descends from Character, but I haven’t further implented Ally yet)

string Character::getIMFileName() { return imageMapFileName; }

How do I make this work? I can’t find a standard API reference for
SDL_image. The only hints I can find are

Load an image from a file.

but I don’t know what ‘file’ is. Is it an SDL class?

IMG_Load may want a const char * instead of a string. try

image[i] = IMG_Load( ally[i].getIMFileName().c_str() );