Reading a string with spaces with sscanf

In C, the sscanf function is used to read formatted input from a string. Typically, sscanf stops reading upon encountering a space, as space is considered the default delimiter for strings. However, if you want to read a string containing spaces, you need to use specific format specifiers in the format string.

For example, if you have a string containing a person's full name with spaces between the name parts, you can use %[^ ] to read the entire line until a newline character is encountered, or %[^ ] until a tab character is encountered, or more commonly, use "%[^"]" to read until another quotation mark. Here, ^ denotes the start of a negated character class, meaning it matches any character except those specified.

Example

Suppose we have the following string, which needs to extract the first and last names:

c
char info[] = "John Smith";
char firstName[100], lastName[100];

// Using sscanf to read a string containing spaces
sscanf(info, "%s %[^
]", firstName, lastName);
printf("First Name: %s\n", firstName);
printf("Last Name: %s\n", lastName);

In this example, %s reads the first word "John" into the firstName variable. %[^ ] reads from the first space until a newline character is encountered, storing the remaining part "Smith" into the lastName variable.

Note that %[^ ] is used here to ensure that strings containing spaces can be read. If you only use %s, it will stop reading upon encountering a space, so you would only get "John".

Important Notes

• When using %[...], ensure that the destination array has sufficient space to store the expected string; otherwise, it may lead to buffer overflow.
• Generally, for safety, it is best to use a maximum width (e.g., %99[^ ]) to avoid buffer overflow due to excessively long strings.
• The return value of sscanf can be used to check the success of the input operation; it returns the number of successfully read input items.

By doing this, you can flexibly extract various formatted data containing spaces from strings.