调用system()返回256 [英] call system() return 256

问题描述

我想用system()在我的应用程序中打印pstack信息，但是它失败并返回256.但是我将下面的代码收集到一个新的主函数中，没关系.为什么?

I want to system() to print pstack info in my application, but it failed and return 256.But I pick up these codes as below to one new main function,that's ok. why?

char cmd[256] ;
string pstackCmd;
struct timeval tv;
struct tm lt;(&tv, NULL);

localtime_r(&tv.tv_sec, &lt);
sprintf(cmd, "pstack `pgrep app` > pstack_%04d%02d%02d%02d%02d%02d%03d",
                            lt.tm_year+1900,
                            lt.tm_mon+1,
                            lt.tm_mday,
                            lt.tm_hour,
                            lt.tm_min,
                            lt.tm_sec,
                            (int)(tv.tv_usec/1000));
pstackCmd = string(cmd);
int retValue = system(pstackCmd.c_str());
if ( retValue != 0)
{
    printf("pstack `pgrep app`,retValue:%d",retValue);
}

推荐答案

代替此:

if (retValue != 0)

您需要这个:

if (retValue == -1 || WEXITSTATUS(retValue) != 0)

也就是说，您首先通过查看 system()是否返回-1来检查是否存在故障；如果没有，则该命令的退出状态(传统上为零表示成功).

That is, you check for failure first by seeing if system() returned -1; if it did not then the exit status of the command (with zero meaning success, traditionally).

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