https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83431
--- Comment #3 from Matteo Croce <mcroce at redhat dot com> --- I can reproduce it with this snippet: void f() { const char *dir = "a"; const char file[50] = "b"; char buf[4]; snprintf(buf, sizeof(buf), "%s/%s", dir, file); } $ gcc -Wall -c buf.c buf.c: In function ‘f’: buf.c:8:33: warning: ‘%s’ directive output may be truncated writing up to 49 bytes into a region of size 3 [-Wformat-truncation=] 8 | snprintf(buf, sizeof(buf), "%s/%s", dir, file); | ^~ ~~~~~~~~~~~ buf.c:8:2: note: ‘snprintf’ output 2 or more bytes (assuming 51) into a destination of size 4 8 | snprintf(buf, sizeof(buf), "%s/%s", dir, file); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ $ gcc -v Using built-in specs. COLLECT_GCC=/usr/bin/gcc COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/9/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-redhat-linux Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux Thread model: posix gcc version 9.1.1 20190503 (Red Hat 9.1.1-1) (GCC) Regards, Matteo Croce