How to Efficiently Verify Prefixes and Convert Substrings to Integers in C ?

Efficiently Verifying Prefixes and Converting Substrings to Integers in C

The need to check if a string begins with a specific prefix and convert a substring to an integer is a common task in programming. In Python, this can be easily achieved using the startswith() and int() functions. However, implementing similar functionality in C requires a different approach.

To check if a C std::string starts with a certain string, you can use the rfind() function with the position parameter pos set to zero. This restricts the search to only match the prefix at the beginning of the string or earlier. For example, to check if argv[1] starts with "--foo=":

if (argv[1].rfind("--foo=", 0) == 0) {
  // argv[1] starts with "--foo="
}

To convert a substring to an integer, you can use the stoi() function. However, since rfind() returns a position, you'll need to extract the substring first. Here's an updated Python pseudocode:

if argv[1].startswith('--foo='):
    foo_value = int(argv[1]['--foo='.len():])

In C , this would translate to:

size_t pos = argv[1].rfind("--foo=", 0);
if (pos != std::string::npos) {
  foo_value = std::stoi(argv[1].substr(pos + 6));
}

This approach is efficient and straightforward, requiring no external libraries or additional complexities. It provides a concise and effective solution for both prefix checking and substring conversion in C .

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