cid ca78c92eeb412f8d74d911909087a86a2d445c53040c4e4439817c5740f79267 · original · open access · via man
Title: qsort(3) - Linux manual page
Authors:
Venue: man
Year: 2008
Canonical: man:man3/qsort.3
URL: https://man7.org/linux/man-pages/man3/qsort.3.html
Collector: man
OA: true
ABSTRACT
qsort(3) - Linux manual page man7.org Linux man-pages Linux/UNIX system programming training qsort(3) — Linux manual page NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON qsort(3) Library Functions Manual qsort(3) NAME top qsort, qsort_r - sort an array LIBRARY top Standard C library (libc, -lc) SYNOPSIS top #include void qsort(size_t n, size_t size; void base[n * size], size_t n, size_t size, typeof(int (const void [size], const void [size])) *compar); void qsort_r(size_t n, size_t size; void base[n * size], size_t n, size_t size, typeof(int (const void [size], const void [size], void *)) *compar, void *arg); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): qsort_r(): _GNU_SOURCE DESCRIPTION top The qsort() function sorts an array with n elements of size size. The base argument points to the start of the array. The contents of the array are sorted in ascending order according to a comparison function pointed to by compar, which is called with two arguments that point to the objects being compared. The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second. If two members compare as equal, their order in the sorted array is undefined. The qsort_r() function is identical to qsort() except that the comparison function compar takes a third argument. A pointer is passed to the comparison function via arg. In this way, the comparison function does not need to use global variables to pass through arbitrary arguments, and is therefore reentrant and safe to use in threads. RETURN VALUE top The qsort() and qsort_r() functions return no value. ATTRIBUTES top For an explanation of the terms used in this section, see attributes(7). ┌──────────────────────────────────────┬───────────────┬─────────┐ │ Interface │ Attribute │ Value │ ├──────────────────────────────────────┼───────────────┼─────────┤ │ qsort(), qsort_r() │ Thread safety │ MT-Safe │ └──────────────────────────────────────┴───────────────┴─────────┘ STANDARDS top qsort() C11, POSIX.1-2008. HISTORY top qsort() POSIX.1-2001, C89, SVr4, 4.3BSD. qsort_r() glibc 2.8. NOTES top To compare C strings, the comparison function can call strcmp(3), as shown in the example below. EXAMPLES top For one example of use, see the example under bsearch(3). Another example is the following program, which sorts the strings given in its command-line arguments: #include #include #include static int cmpstringp(const void *p1, const void *p2) { /* The actual arguments to this function are "pointers to pointers to char", but strcmp(3) arguments are "pointers to char", hence the following cast plus dereference. */ return strcmp(*(const char **) p1, *(const char **) p2); } int main(int argc, char *argv[]) { if (argc ...\n", argv[0]); exit(EXIT_FAILURE); } qsort(&argv[1], argc - 1, sizeof(char *), cmpstringp); for (size_t j = 1; j