There are industry standards for bar coding. Virtually every manufacturer of computers and peripherals for instance has standardized on the Code 3-of-9 (Code 39) format. They have done so for a number of reasons. While most bar code formats are numeric only, Code 39 is an alphanumeric bar code consisting of all uppercase alphas A through Z, numerals 0 through 9, and a half dozen or so punctuation marks. Code 39 is a variable-length bar code. Anywhere from a single character to 30 or more characters (space and scanning hardware permitting) can be in a bar code.
Code 39 is in the public domain, which means that programmers can freely accommodate printing Code 39 in their programs.
UPC is clearly the most visible bar code in the US, and it is also the most useless to 98% of the population. It is a special-purpose bar code that is used by manufacturers whose products will be sold in retail stores with scanning equipment. This pretty much limites UPC to supermarkets and some record stores. UPC is hard to print and there is no reason to do so. Most currently available bar code scanners "autodiscriminate" which means they automatically decode several different bar code formats.