Fórum de discussão

Eu recebi um warning dizendo que eu tinha declarado uma variável e não tinha usado a mesma [-Wunused-but-set-variable], contudo eu usei essa variável no programa. Tanto que quando eu tirei a variável da declaração para ver se desaparecia o warning, deu o erro "undeclared (first use in this function)".

Tem problema esse tipo de warning?

compilando o meu ep com as flags "-Wall -pedantic -ansi -O2" tenho o seguinte warning:
"ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result]"

Para eliminar o warning devido o scanf ou fscanf basta compilar com a opção -Wno-unused-result. Assim, as opções de compilação passam a ser:

-Wall -O2 -pedantic -ansi -Wno-unused-result

A propósito, vejam logo a seguir o que a man page do scanf diz. Os avisos são devidos ao fato de ignorarmos os valores retornados pela função:

meu_prompt> man scanf
SCANF(3)                                                        Linux Programmer's Manual                                                        SCANF(3)

NAME
       scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf - input format conversion

SYNOPSIS
       #include <stdio.h>

       int scanf(const char *format, ...);
       int fscanf(FILE *stream, const char *format, ...);
       int sscanf(const char *str, const char *format, ...);

       #include <stdarg.h>

       int vscanf(const char *format, va_list ap);
       int vsscanf(const char *str, const char *format, va_list ap);
       int vfscanf(FILE *stream, const char *format, va_list ap);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       vscanf(), vsscanf(), vfscanf():
           _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;

DESCRIPTION
       The  scanf() family of functions scans input according to format as described below.  This
       format may contain conversion specifications; the results from such conversions,  if  any,
       are  stored in the locations pointed to by the pointer arguments that follow format.  Each
       pointer argument must be of a type that is appropriate for the value returned by the  cor‐
       responding conversion specification.

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RETURN VALUE
       These functions return the number of input items successfully matched and assigned,  which
       can be fewer than provided for, or even zero in the event of an early matching failure.

       The  value EOF is returned if the end of input is reached before either the first success‐
       ful conversion or a matching failure occurs.  EOF is also returned if a read error occurs,
       in  which case the error indicator for the stream (see ferror(3)) is set, and errno is set
       indicate the error.

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