Asgstr allocates and returns a copy of the string pointed to by s. This function implements string assignment.
Dotrim creates a string from the text between the locations pointed to by u and v, exclusive of v.
Clrstr initializes the header to represent the null string. The null string does not require a text buffer.
Setstr initializes the header to represent a string with length len. If len is non-zero, a text buffer is allocated with malloc(3) and attached to the header. The contents of the buffer are undefined (but its length is guaranteed). Zero is normally returned.
These functions do not directly implement any BASIC functions. These functions support other functions that require BASIC strings.
from The Basmark QuickBASIC Programmerís Manual by Lawrence Leinweber