检查命令行参数不是 char c++

Question

我正在尝试检查命令行参数是字母还是数字

int main(int argc, char* argv[])
{
    if(argv[1] is not int) //How does it check if it is number or alphabets
    { 
        cerr<< "arguments must be integer" << endl;
        return -1;
    }
}

如果我运行在 linux 终端输出会像

./a.out aasmsnsak
arguments must be integer

Answer 1

使用标准库执行此操作的一种方法是使用 <cstdlib> 中的 strtol。另一个使用 istringstream.

char *endptr;
const long int argument = strtol (argv[1], &endptr, 10);  // <cstdlib>
if(endptr[0] != '[=10=]') {
    cerr << "arguments must be integer" << endl;
    return -1;
} else if (argument == LONG_MIN || argument == LONG_MAX) {  // <climits>
    // Alternatively you can check for ERANGE in errno
    cerr << "arguments value is out of range" << endl;
    return -1;
} else {
    /* Right type of argument received */
    [..]
}

Demo using strtol

istringstream iss(argv[1]);
int argument;
char more;
if(iss >> argument) {
    if(iss >> more) {
        cerr << p << ": arguments must be integer" << endl;
        return -1;
    } else {
        /* Right type of argument received */
        [..]
    }
} else {
    cerr << p << ": arguments must be integer" << endl;
    return -1;
}

Demo using istringstream

Answer 2

起初，命令行参数可能存在多个字符。所以你将不得不遍历所有这些：

for(char* arg = argv[1]; *arg; ++arg)

现在我假设您想要将包含 any 非数字字符的字符串分类为非数字，因此在循环内，您将检查每个字符的数字：

if(!isdigit(static_cast<unsigned char>(*arg)))
{
    // non-number-string!

    break; // no need to go on...
}

另一种变体可能只是试图转换为数字：

std::istringstream s(argv[1]);
int n;
s >> n;
if(s) // number read?
{
    char c;
    s >> c;
    if(!s.eof())
    {
        // not last character reached!
        // -> no number
    }
}

或：

char* end;
long number = strtol(argv[1], &end, 10);
//                              ^ needed for detecting, if end of string reached
if(*end || errno == ERANGE)
{
    // doesn't point to terminating null character -> no number
    // or number read was out of range
}

C 风格变体：

int n, int l;
if(sscanf(argv[1], "%d%n", &n, &l) == 1 && argv[1][l] == 0)
{
    // successfully scanned an integer and end of string reached -> is a number
}

检查命令行参数不是 char c++

Check command line arguments is not char c++

c++

command-line-arguments