read file char-by-char
#include <stdio.h> |
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FILE *h; |
int ch; |
h = fopen("filename", "rb"); |
/* error checking missing */ |
while ((ch = fgetc(h)) != EOF) { |
/* deal with ch */ |
} |
/* if needed test why last read failed */ |
if (feof(h) || ferror(h)) /* whatever */; |
fclose(h); |
You can replace fgetc(h) with getchar() to read from standard input.
read file line-by-line
#include <stdio.h>
FILE *h;
char line[100];
h = fopen("filename", "rb");
/* error checking missing */
while (fgets(line, sizeof line, h)) {
/* deal with line */
}
/* if needed test why last read failed */
if (feof(h) || ferror(h)) /* whatever */;
fclose(h); |
Flexible Array Member
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How to declare a FAM? By using empty brackets as the last member of a struct.
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How to define the size for an object containg a FAM? ptr = malloc(sizeof *ptr + sizeof (FAMTYPE[wantedsize]));
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Do not use FAMs! They were known as struct hack before C99 and, now as then, feel like a dirty hack.
<stdio.h> functions with a FILE pointer at the end
char *fgets(char *, int, FILE *); |
int fputc(int, FILE *); |
int fputs(char *, FILE *); |
size_t fread(void *, size_t, size_t, FILE *); |
FILE *freopen(char *, char *, FILE *); |
size_t fwrite(void *, size_t, size_t, FILE *); |
int ungetc(int, FILE *); |
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dynamic memory
Remember to #include <stdlib.h> |
Allocate |
malloc |
ptr = malloc(n * sizeof *ptr); |
calloc |
ptr = calloc(n, sizeof *ptr); |
Change size |
realloc |
newsize = n * sizeof *ptr; tmp = realloc(ptr, newsize); if (tmp) ptr = tmp; else /* ptr is still valid */; |
Release |
free |
free(ptr); |
remove trailing newline
How do I remove the final newline in a string?
len = strlen(data);
if (len && data[len - 1] == '\n') data[--len] = 0;
or, if you don't need to keep and update data length
data[strcspn(data, "\n")] = 0; |
If len is known in advance, do not call strlen(). You can pass the updated len to the caller.
Casting
Casts in C are almost always wrong. When are they right? |
<ctype.h> |
isupper((unsigned char)ch) |
%p printf specifiers |
printf("%p", (void*)ptr) |
Specifically a cast to the return value of malloc() is a definite sign the code author either didn't know what he was doing or didn't choose a good language for the implementation of whatever he's doing.
(BSD) sockets
Headers needed
#include <arpa/inet.h>
#include <netdb.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
initialize with
getaddrinfo()
loop to find and connect a socket
socket()
connect()
if needed: close()
after loop: freeaddrinfo()
getpeername(), getsockname()
send() or recv() or sendto() or recvfrom()
close() |
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Predefined C macros
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__FILE__ "filename.c" or something like that
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__LINE__ 42 or another integer
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__STDC__ 1
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__STDC_VERSION__ undefined for C89; 199901L for C99; 201112L for C11
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__DATE__ "Feb 17 2012" for example
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__TIME__ "15:16:17" for example
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__func__ "main" for example
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__STDC_HOSTED__ 0 or 1
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Reserved identifiers
Reserved for all uses anywhere |
_[A-Z]*; __* |
E[A-Z]*; E[0-9]* |
is[a-z]*; to[a-z]* |
SIG[A-Z]*; SIG_[A-Z]* |
LC_[A-Z]* |
*_t |
str[a-z]*; mem[a-z]*; wcs[a-z]* |
all math functions possibly followed by f or l |
When #include <limits.h> is present |
*_MAX |
When #include <signal.h> is present |
SA_* |
sa_* |
POSIX adds a few other identifiers |
<dirent.h> |
d_* |
<fcntl.h> |
l_*; F_*; O_*; S_* |
<grp.h> |
gr_* |
<pwd.h> |
pw_* |
<sys/stat.h> |
st_*; S_* |
<sys/times.h> |
tms_* |
<termios.h> |
C_*; V_*; I_*; O_*; TC*; B[0-9]* |
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