C String Methods

programming

Strings methods

• printf/scanf - standard i/o stream (stdin, stdout)
• sprintf/sscanf - same but with strings
• sprintf(char* str, const char* format, ...)

char buf[256];
int i = 135;
sprintf(buf, "%d", i);

write down "135" to buf

• sscanf(const char* str, const char* format, ...)
• my_prog -n 256
  • -> argv:
    • pointer to "my_prog\0"
    • pointer to "-n\0"
    • pointer to "256"
    • NULL
• sscanf(argv[2], "%d", &i);
• malloc(i * sizeof(int))

Reading string

#include <stdio.h>

• char* gets(char* buf);
  • read string to buf untill '\n' or EOF
  • never use it
• scanf("%s", buf);
• scanf("%10s", buf);
  • stops with '\n', EOF or 11th symbol
• char* fgets(char* s, int size, FILE* stream);
  • s - link to first symbol
  • size - length of string
  • stream may be connected with file, console,

#include <string.h>
or
#include <cstring>

• str... - watching for string ending markers
• mem... - not watching

Str…

• char* strcpy(char* dst, const char* src);
  • buf = malloc(...)
  • strcpy(buf, "Hello world!")
• char* strncpy(char* dst, const char* src, size_t n);
  • determines length of string
• char* strcat(char* dst, const char* src);
  • not controls memory volume
  • handles '\n' and other
• char* strncat(char* dst, const char* src, size_t n;)
• size_t strlen(const char* s);
  • length of string without '\0' counting
• char* strchr(const char* s, char c);
  • returns first in index
• char* strrch(const char* s, char c);
  • returns last in index
• char* strstr(const char* needle, const char* haystack);
  • returns pointer of first char of needle in haystack
  • substring search
  • searching for needle in haystack
  • NULL if not found
• char* strtok(char* s, const char* delim);
  • tokenize string by delim separator
  • delim -> '\0'
  • delim is char or couple of independent chars
  • example:

  // print the heap array of char
  word = strtok(str, ",");
  while (word != NULL) {
    printf("word: %s\n", word);
    word = strtok(NULL, ",");
  }

• char* strerror(int err_code);
  • returns error code
  • example:
    • int error;
    • int ret_val = func(&error);
    • if (!error) {
    • working with ret_val
    • } else {
    • diagnostics}
• long int strtol(const char* ptr, char** end, int base)
  • ptr - pointer to first symbol of string
  • end - pointer to pointer to end (123na)
  • base - basis of number system

Mem…

• void* memset(void* s, int c, size_t n);
  • set first n symbols of s to little byte of c
  • it’s fast unlike for

Static variables

Global variable declares only in first execution and accessable only from that func

int func() {
	static int x = 10;
	
	return 0;
}

example

int f() {
static int x = 0;
x++;
printf("called %d times\n");
return 0;
}

Global errno variable

#include <errno.h>
 
fopen();
printf("%d", errno);

Not all std functions sets errno to 0

printf("%s", streerror(errno));
 
f = fopen()
if (!f) {
printf("fopen errno\n");
return 1;
}

Transformations strings to …

• int atoi(const char* s)
  • ASCII to int
  • atoi - int
  • atol - long
  • atod - double
  • int a = atoi("123");
  • int a = atoi("b34"); - returns 0 or smth else. it’s error

Standard streams

• stdout
• stdin
• stderr - standard error stream

Examples

1.