NSString to float...what happens if NSString is not numerical and contains alphanumeric characters?

if NSString sample = @"1sa34hjh#@";

Float 64 floatsample = [sample floatValue];开发者_如何学JAVA

what happens? what does floatsample contain?

Read the documentation.

Return Value

The floating-point value of the receiver’s text as a float, skipping whitespace at the beginning of the string. Returns HUGE_VAL or –HUGE_VAL on overflow, 0.0 on underflow.

Also returns 0.0 if the receiver doesn’t begin with a valid text representation of a floating-point number.

The best way to figure out the return value is to check the return value yourself. You can create a small program and save it as a file with a .m extension. Here's a sample:

// floatTest.m
#import <Foundation/Foundation.h>

int main() {
    NSString *sample = @"1sa34hjh#@";
    float floatsample = [sample floatValue];
    printf("%f", floatsample);
    return 0;
}

Compile it on the command-line using clang and linking with the Foundation framework.

clang floatTest.m -framework foundation -o floatTest

Then run the executable and see the output.

./floatTest

The printed value is 1.000000. So to answer your question, if the string starts with a number, then the number portion of the string will be taken and converted to float. Same rules as above apply on overflow or underflow.

If creating the files seems like a hassle, you might like this blog post on minimalist Cocoa programming.