AC_CHECK_FUNC doesn't provide any information about the type of the checked function and just uses "char".
In normal configuration processes, the test compilation produces a warning, but succeeds, if the function is available with a different type. But if you have as CFLAG -Werror, for example if you use start the configure process with CFLAGS+=-Werror ./configure then warning abuot the different types will cause the test to fail despite the function is available. Possible solutions: * Provide the possibility to specify the type of the function * Provide the possibility to specify the header, where the function is defined, when it is available. Greetings Peter Häring