.FromFile won't take string variable as argument.

[Razorhead69]

Hi.

I am trying to change the background image of a form control passing a string variable instead of a litteral string.

Is this possible at all ?

the code i'm trying to use is this:


const std::string test = "C:\\Users\\Pictures\\Tiger.jpg";

Form1.BackgroundImage ->FromFile(test);


many thanks in advance.

[salem c]

Well if a string literal works, then I'm guessing you need something like

Form1.BackgroundImage ->FromFile(test.c_str());

[Razorhead69]

I have tried that, but the only thing that works is ::FromFile("Picturename here");

I tried C_str() but got this errror code:

Form1.BackgroundImage ->FromFile(test.c_str());

no instance of overloaded function "System::Drawing::Image::FromFile" matches the argument list Project2 C:\Users\IT\Source\Repos\Project2\MyForm.cpp


I have 400 pictures my program randomly chooses from.

The problem is that i need to switch pictures on 2 forms using them like slides in powerpoint.

[Thomas1965]

When you write sth. like
this->BackgroundImage = System::Drawing::Image::FromFile("C:\\Temp\\Background.jpg"); than the const char* literal is automatically converted to a System::String^ but it doesn't work work for std::string

The best solution is to stick with System::String^ and forget about the std::string.
To read all the image filenames into an array:
https://docs.microsoft.com/en-us/cpp/dotnet/file-handling-and-i-o-cpp-cli?view=vs-2019

[Razorhead69]

Ok.

That got rid of the error code, but the forms background image doesn't change. ???


I stepped through the program and i can see that the value of backgroundImage is a Nullptr.

What am i doing wrong ?


this is my code so far:



int main()
{

Application::EnableVisualStyles();
Application::SetCompatibleTextRenderingDefault(false);

Project2::MyForm slide1;

System::String^ test = "C:\\Users\\IT\\Pictures\\testpicture.jpg";

slide1.BackgroundImage->FromFile(test);

Application::Run(% slide1)

}

[seeplus]

.c_str() returns a const char* - not char*. If the function requires a char* rather than const char *, then use .data() [for C++17] instead which gives char *. Alternatively cast .c_str() to a char *.

[Razorhead69]

Seeplus.

I am not sure i understand what you are writing.

i am not using .c_str() anywhere in my program.

[Thomas1965]

seeplus, it's right what you write- in C++, but in .NEt things are different.

@OP, try this:
slid1.BackgroundImage = System::Drawing::Image::FromFile("C:\\Users\\IT\\Pictures\\testpicture.jpg");

[Razorhead69]

Thomas1965

That works, but this way the filename is locked. I wan't to use a variable so that i can change the background image when my program is running.

[Razorhead69]

Found the solution myself.

This doesn't work:

slide1.BackgroundImage->FromFile(test);


But this does:

slide1.BackgroundImage = Image::FromFile(test);code


So the code looks like this:

main
{
Project2::MyForm slide1;

System::String^ test;

test = "C:\\Users\\IT\\Pictures\\TestBilleder\\1.jpg";

slide1.BackgroundImage = Image::FromFile(test);

Application::Run(% slide1);

}


Thanks to those who helped me with my problem.

:o)