c - 使用 glib 将数据写入文件

Question

我有一个代码可以写入多个长度为 <length> 的字符在文件中，使用 g_file_set_contents。当我打开文件时，我看到一些奇怪的字符，它们似乎是 ASCII，例如 @&@@。我假设数据可能以 ASCII 格式写入，从二进制转换，所以我使用了一个函数将 ASCII 转换为二进制。执行后还是没有得到任何解决。
这是代码

#include <glib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char** argv) 
{

 FILE *file = g_fopen("Multicore","w");
 gchar *contents = 00001111;
 gchar **contents1 = NULL;
 GError *err = NULL;
 g_file_set_contents ("Multicore", &contents, 8, &err);
 g_assert ((contents == NULL && err != NULL) || (contents != NULL && err == NULL));
 if (err != NULL)
  {
    g_assert (contents == NULL);
    fprintf (stderr, "Unable to read file: %s\n", err->message);
    g_error_free (err);
  } 
 else
  {
    g_assert (contents != NULL);
  }
  int p = g_ascii_digit_value(contents);
  if (g_ascii_isdigit (contents))
    return contents - '0';
  return -1;
  g_printf(" The output is %c \n", contents);
  return 0;
}

我得到正确的输出为

输出为00001111

Answer 1

你确实有很多错误。按照建议使用警告进行编译将有助于将您的注意力转移到需要修复的地方。首先解决最重要的问题(编译器无法找到 g_fopen)，例如:

debug.c:12:2: warning: implicit declaration of function ‘g_fopen’ [-Wimplicit-function-declaration]
  FILE *file = g_fopen("Multicore","w");
  ^
debug.c:12:15: warning: initialization makes pointer from integer without a cast [enabled by default]
  FILE *file = g_fopen("Multicore","w");
           ^

这告诉您缺少包含文件。快速检查会告诉您包括:`

#include <glib-object.h>
#include <glib/gstdio.h>

修复包含后，您会发现许多额外的警告需要解决:

debug.c: In function ‘main’:
debug.c:13:20: warning: initialization makes pointer from integer without a cast [enabled by default]
gchar *contents = 00001111;
                    ^
debug.c:16:2: warning: passing argument 2 of ‘g_file_set_contents’ from incompatible pointer type [enabled by default]
g_file_set_contents ("Multicore", &contents, 8, &err);
^
In file included from /usr/include/glib-2.0/glib.h:50:0,
                from debug.c:1:
/usr/include/glib-2.0/glib/gfileutils.h:91:10: note: expected ‘const gchar *’ but argument is of type ‘gchar **’
gboolean g_file_set_contents (const gchar *filename,
        ^
debug.c:28:3: warning: passing argument 1 of ‘g_ascii_digit_value’ makes integer from pointer without a cast [enabled by default]
int p = g_ascii_digit_value(contents);
^
In file included from /usr/include/glib-2.0/glib.h:81:0,
                from debug.c:1:
/usr/include/glib-2.0/glib/gstrfuncs.h:96:23: note: expected ‘gchar’ but argument is of type ‘gchar *’
gint                  g_ascii_digit_value  (gchar    c) G_GNUC_CONST;
                    ^
/usr/include/glib-2.0/glib/gstrfuncs.h:67:19: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
((g_ascii_table[(guchar) (c)] & G_ASCII_DIGIT) != 0)
                ^
debug.c:29:7: note: in expansion of macro ‘g_ascii_isdigit’
if (g_ascii_isdigit (contents))
    ^
debug.c:30:5: warning: return makes integer from pointer without a cast [enabled by default]
    return contents - '0';
    ^
debug.c:32:3: warning: format ‘%c’ expects argument of type ‘int’, but argument 2 has type ‘gchar *’ [-Wformat=]
g_printf(" The output is %c \n", contents);
^

依次解决每一个问题会让你的程序编译时只对未使用的变量发出警告，这不会影响它的操作:

#include <glib.h>
#include <glib-object.h>
#include <glib/gstdio.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main (int argc, char **argv)
{

    FILE *file = g_fopen ("Multicore", "w");
    gchar *contents = "00001111";
    gchar **contents1 = NULL;
    GError *err = NULL;
    g_file_set_contents ("Multicore", contents, 8, &err);
    g_assert ((contents == NULL && err != NULL)
            || (contents != NULL && err == NULL));
    if (err != NULL) {
        g_assert (contents == NULL);
        fprintf (stderr, "Unable to read file: %s\n", err->message);
        g_error_free (err);
    } else {
        g_assert (contents != NULL);
    }
    int p = g_ascii_digit_value (*contents);
    if (g_ascii_isdigit (*contents))
        return *contents - '0';
    return -1;
    g_printf (" The output is %c \n", *contents);
    return 0;
}

使用

$ ./bin/debug

输出

$ cat Multicore
00001111

根据需要，没有额外的或奇怪的字符。

启用警告的完整编译字符串

我正在使用的笔记本电脑 (openSuSE 13.1) 上的完整编译字符串利用 pkg-config 来保护必要的 include/lib 路径以及库本身。使用的编译字符串是:

gcc -Wall -Wextra -Ofast -o bin/debug debug.c \
`pkg-config --cflags --libs gtk+-2.0`

如果您没有 pkgconfig，则扩展的完整编译字符串(为了便于阅读而插入行继续)将是:

gcc -Wall -Wextra -Ofast -o bin/debug debug.c -pthread -I/usr/include/gtk-2.0 \
-I/usr/lib64/gtk-2.0/include -I/usr/include/pango-1.0 -I/usr/include/atk-1.0 \
-I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/libdrm \
-I/usr/include/libpng16 -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libpng16 \
-I/usr/include/pango-1.0 -I/usr/include/harfbuzz -I/usr/include/pango-1.0 \
-I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/freetype2 \
-lgtk-x11-2.0 -lgdk-x11-2.0 -lpangocairo-1.0 -latk-1.0 -lcairo -lgdk_pixbuf-2.0 \
-lgio-2.0 -lpangoft2-1.0 -lpango-1.0 -lgobject-2.0 -lglib-2.0 -lfontconfig \
-lfreetype