Last modified on Mon Jan 2 21:36:28 2017 UTC.   Improve this page

Why I can’t step into the sprintf() function?

Stepping into any function requires the presence of the debug information. Normally, the implementation of the printf() family of functions is in the standard C library, which does not include debugging information.

However, for common GCC setups, using the open source newlib library, the source code of any function is available; it can be (temporarily) brought into the project and compiled with debugging information.

The newlib sources can be cloned from:

git clone git://sourceware.org/git/newlib-cygwin.git

Create a subfolder in the source folder (for example newlib-libc) and copy the desired files from newlib-cygwin.git/newlib/libc/stdio. You may also need to copy some additional headers, from related folders.

For example, to step into snprintf() and trace::printf(), the following files were required:

$ tree newlib-libc
├── locale
│   └── setlocale.h
├── stdio
│   ├── dtoa.c
│   ├── fvwrite.h
│   ├── local.h
│   ├── mprec.c
│   ├── mprec.h
│   ├── nano-vfprintf.c
│   ├── nano-vfprintf_float.c
│   ├── nano-vfprintf_local.h
│   ├── snprintf.c
│   ├── vfieeefp.h
│   └── vsnprintf.c
└── stdlib
    └── local.h

3 directories, 13 files

For the build to pass, it might be necessary to define some macros; for the above tree, the following definitions were required:


Please note that the newlib sources are far from warning free, and it is recommended to disable any warning checks for the newlib-libc folder.

If the newlib nano version is used (as in the example above), and printing floats is desired, the routines to convert floats need to be explicitly included, by adding -u _printf_float to the linker.