read file char-by-char#include <stdio.h> | | | 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 MemberHow to declare a FAM? By using empty brackets as the last member of a struct. | How to define the size for an object containg a FAM? ptr = malloc(sizeof *ptr + sizeof (FAMTYPE[wantedsize])); |
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 endchar *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 *); |
| | dynamic memoryRemember 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 newlineHow 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. CastingCasts 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) socketsHeaders 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() |
| | Predefined C macros__FILE__ "filename.c" or something like that | __LINE__ 42 or another integer | __STDC__ 1 | __STDC_VERSION__ undefined for C89; 199901L for C99; 201112L for C11 | __DATE__ "Feb 17 2012" for example | __TIME__ "15:16:17" for example | __func__ "main" for example | __STDC_HOSTED__ 0 or 1 |
Reserved identifiersReserved 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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