When to use a Cast or Convert

Question

I am curious to know what the difference is between a cast to say an int compared to using Convert.ToInt32(). Is there some sort of performance gai

Answer 1

string number = "123abc";

int num;

Int32.TryParse(number, out num); // no exception thrown at this call

Convert.ToInt32(number); // exception IS thrown at this call

Answer 2

Cast when it's really a type of int, Convert when it's not an int but you want it to become one.

For example int i = (int)o; when you know o is an int

int i = Convert.ToInt32("123") because "123" is not an int, it's a string representation of an int.

Answer 3

There are a lot of overloads for Convert.ToInt32 that can take for example a string. While trying to cast a string to an int will throw a compile error. The point being is they're for different uses. Convert is especially useful when you're not sure what type the object you're casting from is.

Answer 4

There is one more reason you should use Convert.ToInt32 instead of a cast.

For example:

float a = 1.3f;
float b = 0.02f;
int c = (int)(a / b);
int d = Convert.ToInt32(a / b);`

The result is c = 64 and d = 65

Answer 5

See Diff Between Cast and Convert on another forum

Answer

The Convert.ToInt32(String, IFormatProvider) underneath calls the Int32.Parse (read remarks).
So the only difference is that if a null string is passed it returns 0, whereas Int32.Parse throws an ArgumentNullException.
It is really a matter of choice whichever you use.

Personally, I use neither, and tend to use the TryParse functions (e.g. System.Int32.TryParse()).

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UPDATE

Link on top is broken, see this answer on StackOverflow.

Answer 6

There is another difference. "Convert" is always overflow-checked, while "cast" maybe, depending on your Settings and the "checked" or "unchecked" keyword used.

To be more explicit. Consider the code:

int source = 260;
byte destination = (byte)source;

Then destination will be 4 without a warning.

But:

int source = 260;
byte destination = Convert.ToByte(source);

will give you a exception.