That depends on what you mean by alternative to C. If you are just looking for a "portable assembly" or systems programming language: there were many alternatives.
If you are looking for the systems programming language that has a chance building and running the same source code on multiple different systems then you have to wait until Posix which is tied to C.
Of course you can well argue that once you have Posix, C is not actually required. You just need a language that can call C style functions (this is a trivial exercise for many languages) with compilers for the platforms you are interested in (not trivial, but it is straight forward work that has been done often enough that it is well understood).
Most people mean Posix+C when they say there were no alternatives to C, and in this form they are correct. The other choices may be better for most definitions of better, but there are few alternatives that let you write code and have a chance of it running on something else.
>You don't need POSIX at all if the language has a rich set of libraries.
Agreed, but that increased the cost of porting a language to the new platform. The larger (and richer) the library the more expensive it is. Unless your large library is built on a smaller internal library (like Posix).
Note that I'm arguing that C was the first to really achieve this. I'm not arguing C is the best choice, not am I arguing that the other languages couldn't have reached that. There are other languages (some better than C) that could have done just as well, but for some reason didn't.
That depends on what you mean by alternative to C. If you are just looking for a "portable assembly" or systems programming language: there were many alternatives.
If you are looking for the systems programming language that has a chance building and running the same source code on multiple different systems then you have to wait until Posix which is tied to C.
Of course you can well argue that once you have Posix, C is not actually required. You just need a language that can call C style functions (this is a trivial exercise for many languages) with compilers for the platforms you are interested in (not trivial, but it is straight forward work that has been done often enough that it is well understood).
Most people mean Posix+C when they say there were no alternatives to C, and in this form they are correct. The other choices may be better for most definitions of better, but there are few alternatives that let you write code and have a chance of it running on something else.