NULL值被打印出来

huangapple
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英文:

Reg: NULL value getting printed

问题

请查看以下显示出现奇怪行为的代码部分：

static int call_apab_process()
{
   static char *pcFnctnNm = "call_apab_process";
   int rc = SUCCESS;
   char cmd[4000];
   char pid[11];
   char logDir[2000];
   cmd[0] = '
static int call_apab_process()
{
   static char *pcFnctnNm = "call_apab_process";
   int rc = SUCCESS;
   char cmd[4000];
   char pid[11];
   char logDir[2000];
   cmd[0] = '\0';
   pid[0] = '\0';
   logDir[0] = '\0';
   dbg_indent(pcFnctnNm);
   dbg_print("Entering Into call_apab_process");
   dbg_print("Print Parameters..");
   dbg_print("MY_HOME     :[%s]", getenv("MY_HOME"));
   dbg_print("SESSION_ID    :[%ld]", pvsp_env->sessionid);
   sprintf(cmd, "%s/bin/GQ19apab_DB_auto.sh %ld", getenv("MY_HOME"), pvsp_env->sessionid);
   sprintf(pid, "0%ld", pvsp_env->sessionid);
   sprintf(logDir, "%s/tmp/db", getenv("MY_HOME"));
   dbg_print("cmd :[%s]", cmd);
}

';
   pid[0] = '
static int call_apab_process()
{
   static char *pcFnctnNm = "call_apab_process";
   int rc = SUCCESS;
   char cmd[4000];
   char pid[11];
   char logDir[2000];
   cmd[0] = '\0';
   pid[0] = '\0';
   logDir[0] = '\0';
   dbg_indent(pcFnctnNm);
   dbg_print("Entering Into call_apab_process");
   dbg_print("Print Parameters..");
   dbg_print("MY_HOME     :[%s]", getenv("MY_HOME"));
   dbg_print("SESSION_ID    :[%ld]", pvsp_env->sessionid);
   sprintf(cmd, "%s/bin/GQ19apab_DB_auto.sh %ld", getenv("MY_HOME"), pvsp_env->sessionid);
   sprintf(pid, "0%ld", pvsp_env->sessionid);
   sprintf(logDir, "%s/tmp/db", getenv("MY_HOME"));
   dbg_print("cmd :[%s]", cmd);
}

';
   logDir[0] = '
static int call_apab_process()
{
   static char *pcFnctnNm = "call_apab_process";
   int rc = SUCCESS;
   char cmd[4000];
   char pid[11];
   char logDir[2000];
   cmd[0] = '\0';
   pid[0] = '\0';
   logDir[0] = '\0';
   dbg_indent(pcFnctnNm);
   dbg_print("Entering Into call_apab_process");
   dbg_print("Print Parameters..");
   dbg_print("MY_HOME     :[%s]", getenv("MY_HOME"));
   dbg_print("SESSION_ID    :[%ld]", pvsp_env->sessionid);
   sprintf(cmd, "%s/bin/GQ19apab_DB_auto.sh %ld", getenv("MY_HOME"), pvsp_env->sessionid);
   sprintf(pid, "0%ld", pvsp_env->sessionid);
   sprintf(logDir, "%s/tmp/db", getenv("MY_HOME"));
   dbg_print("cmd :[%s]", cmd);
}

';
   dbg_indent(pcFnctnNm);
   dbg_print("Entering Into call_apab_process");
   dbg_print("Print Parameters..");
   dbg_print("MY_HOME     :[%s]", getenv("MY_HOME"));
   dbg_print("SESSION_ID    :[%ld]", pvsp_env->sessionid);
   sprintf(cmd, "%s/bin/GQ19apab_DB_auto.sh %ld", getenv("MY_HOME"), pvsp_env->sessionid);
   sprintf(pid, "0%ld", pvsp_env->sessionid);
   sprintf(logDir, "%s/tmp/db", getenv("MY_HOME"));
   dbg_print("cmd :[%s]", cmd);
}

以下是输出结果：

Entering Into call_dadp_process
Print Parameters..
MY_HOME     :[/opt/apnp]
SESSION_ID    :[1054628118]
cmd :[]

有人能否指导我了解为什么 cmd 的值显示为空？当我单独打印 MY_HOME 和 session_id 的值时，我确实看到这些值是存在的。

英文:

Please find the code below which is showing some weird behavior

static int call_apab_process()      
{
   static char *pcFnctnNm = "call_apab_process";
   int rc = SUCCESS;
   char cmd[4000];
   char pid[11];
   char logDir[2000];
   cmd[0] = '
static int call_apab_process()      
{
static char *pcFnctnNm = "call_apab_process";
int rc = SUCCESS;
char cmd[4000];
char pid[11];
char logDir[2000];
cmd[0] = '\0';
pid[0] = '\0';
logDir[0] = '\0';
dbg_indent(pcFnctnNm);
dbg_print("Entering Into call_apab_process");
dbg_print("Print Parameters..");
dbg_print("MY_HOME     :[%s]",getenv("MY_HOME"));
dbg_print("SESSION_ID    :[%ld]",pvsp_env->sessionid);
sprintf(cmd,"%s/bin/GQ19apab_DB_auto.sh %ld",getenv("MY_HOME"),pvsp_env->sessionid);
sprintf(pid,"0%ld",pvsp_env->sessionid);
sprintf(logDir,"%s/tmp/db",getenv("MY_HOME"));
dbg_print("cmd :[%s]",cmd);
}
The output is as given below.
Entering Into call_dadp_process
Print Parameters..
MY_HOME     :[/opt/apnp]
SESSION_ID    :[1054628118]
cmd :[]

';
   pid[0] = '
static int call_apab_process()      
{
static char *pcFnctnNm = "call_apab_process";
int rc = SUCCESS;
char cmd[4000];
char pid[11];
char logDir[2000];
cmd[0] = '\0';
pid[0] = '\0';
logDir[0] = '\0';
dbg_indent(pcFnctnNm);
dbg_print("Entering Into call_apab_process");
dbg_print("Print Parameters..");
dbg_print("MY_HOME     :[%s]",getenv("MY_HOME"));
dbg_print("SESSION_ID    :[%ld]",pvsp_env->sessionid);
sprintf(cmd,"%s/bin/GQ19apab_DB_auto.sh %ld",getenv("MY_HOME"),pvsp_env->sessionid);
sprintf(pid,"0%ld",pvsp_env->sessionid);
sprintf(logDir,"%s/tmp/db",getenv("MY_HOME"));
dbg_print("cmd :[%s]",cmd);
}
The output is as given below.
Entering Into call_dadp_process
Print Parameters..
MY_HOME     :[/opt/apnp]
SESSION_ID    :[1054628118]
cmd :[]

';
   logDir[0] = '
static int call_apab_process()      
{
static char *pcFnctnNm = "call_apab_process";
int rc = SUCCESS;
char cmd[4000];
char pid[11];
char logDir[2000];
cmd[0] = '\0';
pid[0] = '\0';
logDir[0] = '\0';
dbg_indent(pcFnctnNm);
dbg_print("Entering Into call_apab_process");
dbg_print("Print Parameters..");
dbg_print("MY_HOME     :[%s]",getenv("MY_HOME"));
dbg_print("SESSION_ID    :[%ld]",pvsp_env->sessionid);
sprintf(cmd,"%s/bin/GQ19apab_DB_auto.sh %ld",getenv("MY_HOME"),pvsp_env->sessionid);
sprintf(pid,"0%ld",pvsp_env->sessionid);
sprintf(logDir,"%s/tmp/db",getenv("MY_HOME"));
dbg_print("cmd :[%s]",cmd);
}
The output is as given below.
Entering Into call_dadp_process
Print Parameters..
MY_HOME     :[/opt/apnp]
SESSION_ID    :[1054628118]
cmd :[]

';
   dbg_indent(pcFnctnNm);
   dbg_print("Entering Into call_apab_process");
   dbg_print("Print Parameters..");
   dbg_print("MY_HOME     :[%s]",getenv("MY_HOME"));
   dbg_print("SESSION_ID    :[%ld]",pvsp_env->sessionid);
   sprintf(cmd,"%s/bin/GQ19apab_DB_auto.sh %ld",getenv("MY_HOME"),pvsp_env->sessionid);
   sprintf(pid,"0%ld",pvsp_env->sessionid);
   sprintf(logDir,"%s/tmp/db",getenv("MY_HOME"));
   dbg_print("cmd :[%s]",cmd);
}

The output is as given below.

Entering Into call_dadp_process
Print Parameters..
MY_HOME     :[/opt/apnp]
SESSION_ID    :[1054628118]
cmd :[]

Can someone please guide me to understand why the value of cmd is displayed as null? When I print the values of MY_HOME and session_id individually I do see that the values are present.

答案1

得分: 3

The translated content is as follows:

sprintf(pid, "0%ld", pvsp_env->sessionid);

绝对越界写入。您的输出显示

SESSION_ID    :[1054628118]

一个包含10位数字的数字。在`sprintf()`中，您添加了一个前导`0`，因此您写入了11个字节+`'
sprintf(pid, "0%ld", pvsp_env->sessionid);

绝对越界写入。您的输出显示

SESSION_ID    :[1054628118]

一个包含10位数字的数字。在`sprintf()`中，您添加了一个前导`0`，因此您写入了11个字节+`'\0'`，总共12个字节，但`pid`只定义为`char pid[11];`

这会在您的情况下引发未定义行为，显然`'\0'`会覆盖`cmd`的第一个字节，并使其成为空字符串（而不是您所述的NULL，这意味着一个NULL指针）。

'`，总共12个字节，但`pid`只定义为`char pid[11];`

这会在您的情况下引发未定义行为，显然`'
sprintf(pid, "0%ld", pvsp_env->sessionid);

绝对越界写入。您的输出显示

SESSION_ID    :[1054628118]

一个包含10位数字的数字。在`sprintf()`中，您添加了一个前导`0`，因此您写入了11个字节+`'\0'`，总共12个字节，但`pid`只定义为`char pid[11];`

这会在您的情况下引发未定义行为，显然`'\0'`会覆盖`cmd`的第一个字节，并使其成为空字符串（而不是您所述的NULL，这意味着一个NULL指针）。

'`会覆盖`cmd`的第一个字节，并使其成为空字符串（而不是您所述的NULL，这意味着一个NULL指针）。
英文: 
sprintf(pid,"0%ld",pvsp_env->sessionid);

definitly writes out of bounds. Your output shows

SESSION_ID    :[1054628118]

a 10 digit number. In sprintf() you add a leading 0 thus you are writing 11 bytes + '\0' makes 12 in total, but pid is only defined as char pid[11];

That invokes Undefined Behaviour in your case the '\0' obviously overwrites the first byte of cmd and makes it an empty string (not NULL as you stated what would mean a NULL pointer)

huangapple
  • 本文由 发表于 2023年5月25日 21:18:20
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