foo.c: In function 'main':
foo.c:7:9: warning: implicit declaration of function 'gets_s'; did you mean 'gets'? [-Wimplicit-function-declaration]
    7 |         gets_s(a);
      |         ^~~~~~
      |         gets
/nix/store/jfkmqz20q8fsaqizcml86adxqyzlwllx-binutils-2.38/bin/ld: /tmp/ccvAZx4J.o: in function `main':
foo.c:(.text.startup+0x12): undefined reference to `gets_s'
/nix/store/jfkmqz20q8fsaqizcml86adxqyzlwllx-binutils-2.38/bin/ld: foo.c:(.text.startup+0x1c): undefined reference to `gets_s'
collect2: error: ld returned 1 exit status

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