Understanding the Limitations of C Strings: char str[128]

The C programming language comes with a unique set of rules and conventions, one of which is the representation of strings. A string in C is an array of characters where the last character is a null terminator ('0'). This design choice can often lead to confusion, especially when working with fixed-size arrays such as char str[128].

Maximum Characters in char str[128]

When you declare a character array like char str[128], it can hold up to 128 characters. However, to store a valid C string, you need to reserve one character for the null terminator. Therefore, the maximum number of characters that can be stored in str is 127.

This is a tricky question because the variable can indeed hold 128 characters, but the last one should be a zero byte. Many other programming languages use a length byte or word to store the length, but C went with this unique approach.

Character Storage and Encoding

Each ASCII character takes up 1 byte. So, a char array of length 128 is a contiguous memory of 128 bytes, which can store exactly 128 ASCII characters. However, C strings require an additional byte for the null terminator.

Modern programming languages often use Unicode, which can use 2 bytes for characters in its basic form and 8, 16, or 32 bits for more complex characters. This flexibility in encoding means that the exact number of characters that can fit into char str[128] might vary based on the encoding used.

Handling C Strings in Practice

When reading a string from the input stream, the array will carry the characters and be automatically appended with a null terminator if the string length is less than 127. For example, if you enter a string of length 5, it will take 5 characters and 1 null terminator, totaling 6 bytes. Hence, always ensure there is an extra cell for the null terminator. If you are not using the array as a string, you will read each character separately and won't have a terminating null.

Most standard library functions that deal with character strings expect the characters to be located in contiguous memory bytes and the last memory byte to be filled with NULL (0). This design decision, often referred to as NUL-terminated strings, is made to avoid passing around the length of the arrays or passing start pointer and end pointer in order to handle strings effectively.

Conclusion

In summary, when working with a char str[128], you can store up to 127 ASCII characters, reserving the last byte for the null terminator. Understanding how C handles strings, including the use of the null terminator and correct encoding, is crucial for effective programming.

References

1. C Reference - String and Byte

2. C Programming - String Handling

3. GeeksforGeeks - String Handling in C