C - valgrind给出大小为1的无效读取

Question

关于相同的错误代码，我已经经历了几个类似的问题，最关心的是传递无效的指针地址作为返回。然而，这看起来不是这里的情况，因为我的程序正确地处理返回的任何地址。

format_string:

static char *format_string(char *string)
{
    int i;
    if (string == NULL) {
        return string;
    }
    string[0] = (char)toupper((int)string[0]);
    111->for (i = 1; string[i] != ''; i++) {
        if (!isalpha(string[i-1])) {
            string[i] = (char)toupper((int)string[i]);
        } else {
            string[i] = (char)tolower((int)string[i]);
        }
        if (string[i] == '/' || string[i] == '\') {
        string[i] = ' ';
        }
    }
    /* Remove End of string White Spaces */
    while (string[--i]==' '); string[++i]='';
    return string;
}

metadata_extract:

static int metadata_extract(const char *filename, struct kw_metadata *s)
{
    char *memchar = NULL;
    s->obj = NULL;
    s->do_cleanup = &do_on_cleanup;
    if (!is_of_type(filename)) {        
        return KW_ERROR;
    }
    TagLib_File* file = taglib_file_new(filename); 
    TagLib_Tag* tag = taglib_file_tag(file);
    s->type = strdup("Audio");
    s->tagc = 4;
    s->tagtype = (char **)malloc(4 * sizeof(char *));
    s->tagv = (char **)malloc(4 * sizeof(char *));
    memchar = strdup("title");
    s->tagtype[0] = memchar;
    memchar = strdup("artist");
    s->tagtype[1] = memchar;
    memchar = strdup("album");
    s->tagtype[2] = memchar;
    memchar = strdup("genre");
    s->tagtype[3] = memchar;
    153->memchar = strdup(taglib_tag_title(tag));
    memchar = format_string(memchar);
    s->tagv[0] = memchar;
    memchar = strdup(taglib_tag_artist(tag));
    memchar  = format_string(memchar);
    s->tagv[1] = memchar;
    memchar = strdup(taglib_tag_album(tag));
    160->memchar = format_string(memchar);
    s->tagv[2] = memchar;
    memchar = strdup(taglib_tag_genre(tag));
    memchar = format_string(memchar);
    s->tagv[3] = memchar;
    s->obj = file;
    s->do_init = &do_on_init;
    s->do_cleanup = &do_on_cleanup;
    taglib_tag_free_strings();
    taglib_file_free(file);
    return KW_SUCCESS;
}

valgrind:

==16769== Invalid read of size 1
==16769==    at 0x5317605: format_string (plugin_taglib.c:111)
==16769==    by 0x531781F: metadata_extract (plugin_taglib.c:160)
==16769==    by 0x405EB3: metadata_extract (metadata_extract.c:36)
==16769==    by 0x403351: add_metadata_file (dbbasic.c:221)
==16769==    by 0x4032D5: add_file (dbbasic.c:174)
==16769==    by 0x406485: import_semantics (import.c:97)
==16769==    by 0x406440: import_semantics (import.c:92)
==16769==    by 0x4065AC: import (import.c:127)
==16769==    by 0x401916: main (kwest_main.c:87)
==16769==  Address 0x6f4ce11 is 0 bytes after a block of size 1 alloc'd
==16769==    at 0x4C2B3F8: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16769==    by 0x57A6D71: strdup (strdup.c:43)
==16769==    by 0x531780F: metadata_extract (plugin_taglib.c:159)
==16769==    by 0x405EB3: metadata_extract (metadata_extract.c:36)
==16769==    by 0x403351: add_metadata_file (dbbasic.c:221)
==16769==    by 0x4032D5: add_file (dbbasic.c:174)
==16769==    by 0x406485: import_semantics (import.c:97)
==16769==    by 0x406440: import_semantics (import.c:92)
==16769==    by 0x4065AC: import (import.c:127)
==16769==    by 0x401916: main (kwest_main.c:87)

Answer 1

In

for (i = 0; string[i] != ''; i++) {
    if (string[i-1]) {

您正在读取string[-1]，通常是大小为1的无效读取。

你大概是指

for(i = 1; ...

---

编辑后

:

在循环之前，您应该检查字符串在结束前至少有一个字符，

if (string[0] == 0) return string;

(最好在string[0] = (char)toupper((int)string[0]);之前完成)。消息

地址0x6f4ce11在分配大小为1的块后为0字节

告诉你其中一个strdup ed字符串是空的(大小为1的块意味着只分配了0结束符的空间)。

划掉尾随空格后，

while (string[--i]==' '); string[++i]='';

你不检查索引是否有效，如果整个字符串由空格组成，你至少读到string[-1]，你应该检查:

while(i-- > 0 && string[i] == ' ');
string[++i] = 0;

Answer 2

在实际使用变量之前尝试使用if (NULL != memchar)进行验证;否则strdup和函数一样会给出不可预测的结果。