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Full Discussion: valid code?
Top Forums Programming valid code? Post 302093590 by Corona688 on Friday 20th of October 2006 01:29:41 PM
Old 10-20-2006
Quote:
Originally Posted by bebop1111116
Are any of these lines valid code?
i;
Only if there is a variable 'i' declared in scope. But while valid, it's totally useless, the statement has no effect.
Quote:
short int s;
long int L;
long long LL;
The first two are valid. 'long int' is redundant, since 'long L' will declare the same type of variable. The actual sizes of the integers varies from platform to platform, but the order of sizes is always:

sizeof(char) <= sizeof(short) <= sizeof(int) <= sizeof(void *) <= sizeof(long)

Note how sizeof(int) isn't guaranteed to be equal to siezof(void *) -- it can also be smaller. It's usually the same on 32-bit platforms, but assuming it's safe to cast pointer to int has caused many headaches on 64-bit systems, where pointers are suddenly twice as large!

If fixed sizes are needed for integers, like a guaranteed 32-bit type, use the types declared in stdint.h.

'long long' is a gcc extension for 64-bit integers on 32-bit platforms. Different compilers have different ways of doing this. Again, use the 64-bit type from stdint.h instead.
 

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SYSINFO(2)						     Linux Programmer's Manual							SYSINFO(2)

NAME
sysinfo - return system information SYNOPSIS
#include <sys/sysinfo.h> int sysinfo(struct sysinfo *info); DESCRIPTION
sysinfo() returns certain statistics on memory and swap usage, as well as the load average. Until Linux 2.3.16, sysinfo() returned information in the following structure: struct sysinfo { long uptime; /* Seconds since boot */ unsigned long loads[3]; /* 1, 5, and 15 minute load averages */ unsigned long totalram; /* Total usable main memory size */ unsigned long freeram; /* Available memory size */ unsigned long sharedram; /* Amount of shared memory */ unsigned long bufferram; /* Memory used by buffers */ unsigned long totalswap; /* Total swap space size */ unsigned long freeswap; /* Swap space still available */ unsigned short procs; /* Number of current processes */ char _f[22]; /* Pads structure to 64 bytes */ }; In the above structure, the sizes of the memory and swap fields are given in bytes. Since Linux 2.3.23 (i386) and Linux 2.3.48 (all architectures) the structure is: struct sysinfo { long uptime; /* Seconds since boot */ unsigned long loads[3]; /* 1, 5, and 15 minute load averages */ unsigned long totalram; /* Total usable main memory size */ unsigned long freeram; /* Available memory size */ unsigned long sharedram; /* Amount of shared memory */ unsigned long bufferram; /* Memory used by buffers */ unsigned long totalswap; /* Total swap space size */ unsigned long freeswap; /* Swap space still available */ unsigned short procs; /* Number of current processes */ unsigned long totalhigh; /* Total high memory size */ unsigned long freehigh; /* Available high memory size */ unsigned int mem_unit; /* Memory unit size in bytes */ char _f[20-2*sizeof(long)-sizeof(int)]; /* Padding to 64 bytes */ }; In the above structure, sizes of the memory and swap fields are given as multiples of mem_unit bytes. RETURN VALUE
On success, sysinfo() returns zero. On error, -1 is returned, and errno is set to indicate the cause of the error. ERRORS
EFAULT info is not a valid address. VERSIONS
sysinfo() first appeared in Linux 0.98.pl6. CONFORMING TO
This function is Linux-specific, and should not be used in programs intended to be portable. NOTES
All of the information provided by this system call is also available via /proc/meminfo and /proc/loadavg. SEE ALSO
proc(5) COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2017-09-15 SYSINFO(2)
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