Geek Answers Handbook

Pclose () in a file descriptor opened with popen () returns errno 10 (without child processes)

I am running linux and I am trying to do the following:

  • Run ls in the current directory (using popen)
  • Print the result to the buffer (using fread from the channel descriptor)
  • close the pipe (using pclose).

Everything works fine (the buffer is filled correctly with the result ls), but when I check the Result pclose () returns -1, and errno - 10 (without child processes). I don’t know why this is happening, but I cannot ignore it (unless there is a reasonable explanation of why this is happening).

My code is:

FILE * lsoutput = NULL; lsoutput = popen("ls -ltr", "r"); if (readFromPipeOrFile(lsOutput, pSendBuf, pSendActualSize) == -1) { printf("readFromPipeOrFile failed."); pclose(lsOutput); safeFree(pSendBuf); return -1; } if (pclose(lsOutput) == -1) // No idea why it returns -1 but it does... { printf("pclose failed"); printf("errno: %d\n", errno); printf("strerror: '%s'", strerror(errno)); return -1; }

ReadFromPipeOrFile code (buffer write function):

 int readFromPipeOrFile(FILE * pipeOrFile, char ** pSendBuf, size_t * pSendActualSize) { int multiplication = 1; char * pSendBufCurrentLocation = NULL; ERR_RETURN(pipeOrFile == NULL || pSendBuf == NULL || pSendActualSize == NULL, "No values should be NULL."); ERR_RETURN(*pSendBuf != NULL, "*pSendBuf should be NULL"); *pSendBuf = (char *) calloc (MAX_READ_FROM_STREAM * multiplication, sizeof(char)); ERR_RETURN(*pSendBuf == NULL, "Failed allocating sendBuf"); pSendBufCurrentLocation = *pSendBuf; while (fread(pSendBufCurrentLocation, MAX_READ_FROM_STREAM, 1, pipeOrFile) == 1) { ++multiplication; *pSendBuf = realloc(*pSendBuf, MAX_READ_FROM_STREAM * multiplication); ERR_RETURN(*pSendBuf == NULL, "Failed re-allocating sendBuf"); pSendBufCurrentLocation = *pSendBuf + (MAX_READ_FROM_STREAM * (multiplication - 1)); memset(pSendBufCurrentLocation, '\0', MAX_READ_FROM_STREAM); } ERR_RETURN(!feof(pipeOrFile), "Hasn't reached eof but fread stopped"); ERR_RETURN(ferror(pipeOrFile), "Error in fread"); *pSendActualSize = MAX_READ_FROM_STREAM * multiplication; return 0; }

Thanks in advance! EDIT: ERR_RETURN is just a macro that checks if the condition of the first parameter is true, and if so, type a line in the second parameter and return -1. A.

+4
source share
2 answers

According to the documentation for pclose() , it returns -1 if wait4 returns an error. However, it does not say anything about installing errno (other than installing ECHILD if it could not get the child status), so I'm not sure if you can rely on the string strerror() being accurate.

It is assumed that ls exited with an error code that would imply that ls had problems accessing the subdirectory (permission error?). So, you have the results, because ls returned what it could read, but it is incomplete reading, because it could not access the subdirectory in recursion.

0
source

the signal (SIGCHLD, SIG_IGN) will cause the result of pclose () to return -1, and errno to be set to 10 (without child processes).

0
source

More articles:


All Articles