如何在C ++中检查来自editText的输入是否为整数

Question

I want to validate the input from Edit Text, if the input is not integer, Message Box or Show Message will appear, i use

if(input->Text.ToIntDef(1)){
  //instruction
}

but when i run the app, if condition always true , even though i input integer in the Edit Text(i input 5000, 4500, 7000, 7500, 2000, 2500)

Answer 1

A simple method, could be to scan the content of the string, if you detect anything that is not a digit, you can stop the scan and assume that the number is not an integer.

bool is_integer(const char* input) {
    while(*input) {
        if (*input < '0' ||  *input > '9') {
            return false;
        }
        ++input;
    }
    return true;
}

The simple approach above considers an empty string an integer as well, it is a simple matter to change that. Further more any white space in the input will cause the function to treat the input as not being an integer, if you want white spaces to be ignored, you can trim the input before passing it to the function.

From your example I get a suspicion that you are using the VCL-like framework: FireMonkey from C++ Builder, this framework has a method on its default string class called ToInt as far as I recall (without the Def suffix) which will attempt to parse the string as an integer, if unable to, it will throw an EConvertError exception, which you can then basically just catch.